Practical Automotive Electronics

 

PRACTICAL

AUTOMOTIVE ELECTRONICS

by L. David Likes

 

Copyright © L. David Likes, 1995, 2022 All rights reserved Interior Design and Artwork by L. David Likes, ldl-001 Published by: L. David Likes, email address: [email protected]

REGARDING THESE MANUAL MATERIALS The Author, Publisher or Seller assume no liability with respect  to the use of the information contained herein

 

 Dedicated to the man who taught t aught me learning could be fun, William Blair, my Automotive  Instructor.

 

 About the Author 

Dave Likes received a 2-year diploma in Auto Mechanics at Northern Kentucky State Vocational Technical School and a B.S. in Mechanical Engineering Technology at the University of Cincinnati. He became an Automotive Training Instructor for Toyota and worked in both the Cincinnati and Los Angeles Regional Ofces Ofces before starting his Portrait and Wedding Photography Business. In 2014 he became a Certied Professional Photographer with the PPA. Dave is currently semi-retired and teaches photography through private instruction.

 

INTRODUCTION

 Practical Automotive Electronics is designed to pick

up where traditional Automoti Automotive ve Electronic courses leave off. Still, it

is intuitive enough that someone without any background in Automoti Automotive ve Electronics will be able to understand. Emphasi Emphasiss is put on concepts (basic ideas) as opposed to the traditional mathematical approach that most rst-year Electronics students suffer through. As an Automotive Automotive Instructor for Toyo Toyota, ta, for many years, I've seen an ever-increasing gap in the need for an easier way to understand, diagnose and repair advanced electronic and microprocessor systems. This manual is designed to bridge that gap. First, you learn theory and then you learn to apply what you learned to the vehicle. If you've ever taken a long trip you know how important it is to have a road map and know how to read it. Knowing this and having some logic will get you to your destination quickly and with little hassles. Chapter one starts off with the ner   points of reading the road map (Electrical Wiring Diagram). Diagram). Then I'll proceed to show you a practical approach to how electrons travel and how to identify which road they took (if any!) Chapter two deals with the easiest measuring quantity for that, voltage. All abbreviati abbreviations ons are listed in the appendix. Chapter 3 deals with the understanding of AC signals. It is a subject few automotive manuals manuals deal with properly (yet it is a "must subject") to diagnose and solve electronic problems. Chapters 4 and 5 explain solid state components and their relationship to power in an easy-to-unde easy-to-understand rstand way. way. Also included are a simple method for reading logic circuits which is used to diagnose circuit problems. In Chapter 6, you'll learn a specic diagnostic procedure to get you through your travels quickly, using the fastest road possible. It is recommended that you answer the quiz questions at the end of each chapter as they are designed to enhance your understanding of the material as well as test your knowledge of it. I copyrighted the book in 1995 after writing the rst 6 chapters, but never fully published it. The material still applies to today’s vehicles but needed an OBD II update. When the pandemic of 2020 hit, I nally found the time to complete the changes, including how to use the latest aftermarket bi-directional scan tool by Autel, which is the MS-906BT MS-906BT.. To compliment the book’s previous material, I've added Chapter 7 which includes much-needed practical applications to the book helping with the advent of multiple automotive innovations that are being introduced on newer vehicles. Now you'll need your wiring diagrams, even more! I've included a little bit on how each new system works along with how to use the right test techniques, (including engine performance troubleshooting), to diagnose the problem and get the job done quickly and efciently. Lastly, I've added a diagnostic primer section on multiplexing, specic to high-speed can systems, which is the most common and must know know.. L. David Likes September 2022

 

Table of Contents Chapter 1

3

SYMBOLS, COMPONENTS AND WIRE CONNECTI CONNECTIONS ONS ........... ....................... ....................... ...................... ....................... ....................... ....................... ...................... ..........3 3 Headlight, Turn Signal and Tail light Switches ...................... ................................. ....................... ....................... ...................... ....................... ....................... ....................3 .........3 Identifying Pin Numbers ...................... Identifying ................................. ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ......................5 ...........5 Overlapping Wires................. Wires............................ ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ...............6 ...6 Wiring Color Codes........... Codes ...................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ...................7 .......7 Symbols ....................... .................................. ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... .............7 ..7 Junction Blocks.......................... Blocks..................................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... .............. ... 7 Wire to Wire Connectors.............. Connectors......................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ............. 8 Back probing Connectors............ Connectors....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ............. 8 Wire to Component Component Connector Connectors s .......... ..................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .............. ... 8 Grounds.............. Grounds.. ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ................ ..... 9 Fuses and Fusible Links.............. Links.......................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ...................9 .......9 Cartridge Design Fusible Links ............ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ....................9 .........9 Circuit Breakers............... Breakers.......................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ...................10 .......10 Relays and Electromagnetism Electromagnetism ............ ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................10 .........10 Creating a Larger Electromagnetic Electromagnetic Field .......... ..................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ................10 .....10 Additional Addition al Electronic Symbols................ Symbols........................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... .................12 .....12 Chapter 1 Quiz ....................... .................................. ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .............15 ..15

Chapter 2

17

VOLT VOL TAGE DIVIDER CIRCUITS................................ CIRCUITS............................................ ....................... ...................... ....................... ....................... ...................... ....................... ....................... .................. ....... 17  Potentiometers Potentiom eters and Rheostats ........... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................17 .........17 Rheostats ........... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .............. ... 17 Potentiometers Potentiomet ers ....................... .................................. ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ................ ..... 19 Voltage Drops ...................... ................................. ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ...............21 ...21 Capacitors.............................. Capacitors.................. ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .............22 ..22 How to test a Capacitor.. Capacitor.............. ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ............. 23 Old Style Gauges........................ Gauges.................................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ...................24 .......24 Chapter 2 Quiz ....................... .................................. ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .............27 ..27

Chapter 3

29

 ALTERNA  AL TERNATING TING SIGNALS AND SENSORS ............ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .................... ......... 29 ALTERNA AL TERNATING TING SIGNALS ....................... .................................. ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ...................29 .......29

 

OPTICAL SENSORS ...................... .................................. ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ................ ..... 32 Optical Sensor Disadvantage..................... Disadvantage................................ ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... .............. ... 35 MAGNETIC RELUCTANCE POSITION SENSOR ................................................................................................ 36 KNOCK SENSORS........ SENSORS.................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ...................... ........... 37 MAP SENSORS.............................. SENSORS.......................................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ................ ..... 38 OXYGEN SENSORS ........... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ................ ..... 39 ZIRCONIA OXIDE SENSORS ............ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ................... ....... 39 TITANIA TIT ANIA OXIDE SENSORS........................... SENSORS...................................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ................... ....... 40 Chapter 3 Quiz ...................... ................................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... .............. ... 41

Chapter 4

43

SEMICONDUCTORS................. SEMICOND UCTORS............................. ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ................. ...... 43 DIODES....................... DIODES........... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ............... ... 43 Checking Diodes ....................... .................................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ............... ... 44 Despiking Diodes ....................... .................................. ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .................... ......... 46 ZENER DIODES............. DIODES......................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ...................... ........... 47 LIGHT EMITTING DIODES..................... DIODES................................ ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .................... ......... 49 TRANSISTORS................ TRANSIST ORS............................ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... .................... ......... 50 PHOTO TRANSISTORS TRANSISTORS ...................... .................................. ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ................. ..... 54 Chapter 4 Quiz ...................... ................................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... .............. ... 55

Chapter 5

57

INTEGRATED INTEGRA TED CIRCUITS ...................... ................................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ................. ...... 57  OPERATIONAL OPERA TIONAL AMPLIFI AMPLIFIERS ERS ...................... ................................. ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... .............. ... 59 LOGIC CIRCUITS ...................... ................................. ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ...................... ........... 61 AND GATES......... GATES..................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ............... ... 62 Other Logic Symbols and their Tru Truth th Tables .......... ...................... ....................... ...................... ....................... ....................... ....................... ....................... ................ ..... 66 Chapter 5 Quiz ...................... ................................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... .............. ... 69

Chapter 6

71

DIAGNOSTIC DIAGNOST IC PROCEDU PROCEDURE RE ........... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... .......................71 ...........71 5 STEP SYSTEMA SYSTEMATIC TIC DIAGNOSIS................................ DIAGNOSIS........................................... ...................... ....................... ....................... ...................... ....................... ....................... .................. ....... 71 FINDING A SHORT CIRCUIT ........... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... .............. ... 72 INTERMITTENT INTERMIT TENT PROBLEMS................... PROBLEMS.............................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... .................. ....... 73 02 SENSOR MONITOR MONITOR CHECK..... CHECK................. ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ................ ..... 74 Chapter 6 Quiz ...................... ................................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... .............. ... 75 ABBREVIATIONS ABBREVIA TIONS AND GLOSSAR GLOSSARY Y OF TERMS........... TERMS...................... ....................... ....................... ...................... ....................... ....................... ...................... .................. ....... 76 CHAPTER QUIZ QUESTION QUESTION ANSWERS ........... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .................. ....... 78

 

Chapter 1

SYMBOLS,, COMPONEN SYMBOLS COMPONENTS TS AND WIRE  WIRE  CONNECTIONS  Headlight, Turn Signal and Tail light Switches Electrical Wiring Diagrams (or EWD’s for short) use a combined combin ed switch to indicate indicate all modes of operation for any of the vehicle light switch combinations. This is very confus confusing ing to some Autom Technicians Techniat cians the time switch switch initially appears to Automotive operateotive all circuits the as same (which it does not). Take a Toyota Corolla Combination Switch for example:

Combined Light and  Highbeam Switch Note: When reading the tail lights across, they do not align or connect to any external wires, therefore, they do not  apply on this diagram  page. The Toyota EWD Manual shows the taillights diagram in detail  on a separate page.

Read the switch across (horizontally). Read only in one specic rectangle at a time. Next the circles indicate an up and down (vertical) external wire connection to the internal wire in the switch IN THAT SPECIFIC HORIZONTAL MODE ONLY.

 

4

SYMBOLS, COMPONENTS AND WIRE CONNECTIONS

In High Beam Mode the external connections nectio ns are as shown:

Only read  across horizontally in this high beam mode

Look for external wire connections both high and low vertically in each rectangle with an exterior circle attached. Let' s look at the headlight beams being applied. applied. This is the last position at the bottom of the switch. Since there are two circles connected to the internal wire this means that there are two connections. Now which external wire connections are there? Look vertically for this information. There is only one wire connection 9C at the bottom that aligns with the rst circle. At the end of the internal wire there is only one circle aligned with the wire at the top of the switch 12C. Consequently Consequently,, we only have these connections connections during high beam operation.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

CHAPTER 1

Identifying Pin Numbers

Numbering Sequenc Sequence e is different for a male versus a female connector 

One of the most helpful things to understand understand in reading reading EWD’s is being able to determine an exact pin number in a specic wiring connector. Pull the connector apart showing one half of the connector with male pins and the other half  with female pins. The wiring diagram may show one or both halves of the connector. The problem is if you identify the mirror image connector you’ll be identifying the wrong pin number. Example: Pin 1 on connector A would be pin 3 on connector B.

The best way to identify the connector is to look and see if  you have an inner male or female connector in your hand.  Note: Look at the inner male or female pin, not the outer  connector lock. The outer connector lock should be on top when reading pin pin numbers. Always look into the broken broken apart connector straight at the pin for correct numbering sequence.

Male Connector 

Female Connector 

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

5

 

6

SYMBOLS, COMPONENTS AND WIRE CONNECTIONS

 Now the wiring diagram manual does not show any picture of male or female pins. It just numbers the pins. So how can one determine if he or she is looking at the male or female  pin connector? Look L ook at the pin numbering sequence. •   A numbering sequence sequence starting starting on the right right side of of the connector connec tor and moving left is a male connector. connector.

Remember with Male Pins #1 starts on the far top right side

•   A numbering sequence sequence star starting ting on the left side of the the connector conne ctor and moving right is a female connector. connector.

After breaking the connector apart, you should look at the female connector starting with pin 1 being at the top left side of the connector.

RULE: MALES ARE ALWAYS RIGHT! A simple way to remember that pin 1 starts in the upper right hand corner of the male connector is shown in the box above.

Female

If you are looking at the female connector then pin 1 would start on the other side.

Overlapping Wires Modern day wiring diagrams have overlapping overlapping wires as shown below: •   Wires Wires crossed crossed in this this manner do do not connect. connect. •   The only time that overlapping overlapping wires wires connect connect is when a  black dot connects them. This is a splice connection.

EWD COLOR CODES B = Black    L = Blue BR = Brow Brown n LG = Li Ligh ghtt Gree Green n G ==Green GR Gray

   

0 =POrange = Pink 

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

  

R = Red V=Violet W=White Y=Yellow

 

CHAPTER 1

W-R

Wiring Color Codes Wiring diagrams have their own color codes. Code letters separated separ ated by a hyphen indicate a two-tone two-tone stripped wire. Example: R-B  is a red wire with a black stripe. The rst code Letter is the main (or base) color of the wire where the second letter after the hyphen indicates the stripe. Example:  W-R  has white and red colors but white is the base color. Therefore red is the stripe.What color is the stripe in L-W? White is the correct answer.

Symbols When looking looking at the EWD' s you are likely likely to see four re peating types of symbols. They designate different connections in the wiring harness and make it easier for you to nd their location. designates a connection connection to a junction junction block or to •   The oval designates a relay block.

Junction Blocks

A junction block is typically a box where there are several splice connections in the wiring harness thereby reducing the length of several wires. Sometimes a junction block incorporates fuses and a few relays. This shows the internal internal connections connections of the wiring diagram J/B No.l.

 Note that (1F) is a different junction block connector than (1D)  but since they all have the 1 in front they all belong to J/B no. 1. diagram shows shows a specic specic pin number number for a spe•   Also the diagram cic connector.

In the actual wiring diagram there will be an added arrow to the circuit. arrow indicates indicates the male pin. pin. •   The arrow The J/B contains the male pin since the arrow is closest to the J/B. Consequently the connector to the J/B contains the female pin. Knowing which side of the connector you are on becomes extremely important when diagnosing problems.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

7

 

8

SYMBOLS, COMPONENTS AND WIRE CONNECTIONS

Wire to Wire Connecto Connectors rs rectangle indicates a wire to wire connector. •   The rectangle

7

Which pins are the male pins? You should be able to determine this just by looking at the numbering sequence (hint: Wire to Wire Connector  males are always right). The connector right contains the male pins. This connector has wireon onthe both sides of the connector. Looking at the wiring diagram, specically in the specic systems section of  the EWD, the connector will look like this.

C1

Again the arrows indicate the male pin side of the connector. Another point I might add here is that since the pin number is 7 we have at least 7 other pins in connector C1 and possibly more.. You won' t really know until you look at the connector  more connector  comparing the pin number sequence in the EWD.

Female and Male Connector Numbering  Sequences

Back probing Connectors Any connector is a good place to tap into the circuit with a VOM Meter. Keep in mind there is a right way and a wrong way to do it. It is a good idea to "back probe" any connector  regardless of being split open or not.

Will do damage checking on pin side

Safer to Back Probe

Switches Wire to Component Connectors •   The round indicates connection connection to a "part" in the electrical system. Sometimes more than one variation of connector exists on the car. An automatic transmission will show a different connector pin number compared to a manual transmission  pin. In this case the wiring diagram shows both variations at the same time.

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

9

CHAPTER 1

Grounds The triangle indicates a ground connection to the chassis.  Numbering each ground makes it easier to identify it specically from other grounds. Get ground locations by looking in other sections of the EWD Manual.

Fuses and Fusible Links Without short circuit protection of the electrical circuit many wires in the harness could melt together together causing the harness harness to become ruined. Technicians sometimes fail to differentiate  between fuses, fusible links and circuit breakers. You can see the symbol for the fuse. Each fuse has an amperage capacity marked on it for re placement purposes. You' Y ou' ll nd fuses in more than one  junction block location. Always replace the specic fuse with a size of equal amperage capacity. The fusible link differs in symbol as you see. One (or fusible link may branch off to several circuits at the fuse  box junction block). The T he fusible link consequently protects the circuit from the battery to the fuse box. Since many circuits branch off just the one wire it is much thicker in diameter to handle the amperage capacity. •   Fusible link link wire, which is is smaller than than standard standard fuse box box wire, will burn up when exceeding its rated amperage.

Cartridge Design Fusible Links Cartridge Design Fusible Links are more popular in late model vehicles. They contains an acrylic color coded cover.

Fusible Link Capacity  Amps

Fusible Fusibl e Link Cartr Cartridge idge

Cartridge Equivalent Fusible Link Color  Section Area

30 40 50 60 80

0.3 0.5 0.9 1.0 1.3

PINK GREEN RED YELLOW BLACK

100

2.0

BLUE

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

10

SYMBOLS, COMPONENTS AND WIRE CONNECTIONS

Circuit Breakers See the symbol for the circuit breaker. Circuit breakers replace fuses to protect varying power circuits such as heaters, power windows and power sunroof circuits. When the circuit breaker meets its rated value it opens the circuit temporarily. Therefore the circuit breaker is reusable. Many motorized circuits circuits when run the length length of their travel, such as power windows, will cause the motor to lock up (which is normal). Holding down the power window button, while the window is all the way down, causes higher amperage in the circuit and thereby trigging the circuit breaker. Typically small amperage circuit breakers of 7.5 amps have their breakers automatically reset. Circuit breakers containing 10 amps or higher may have a manual reset. In this case there will be a small hole in the cover where one can use a small  probe to reset the circuit breaker.

Relays and Electromagnetism A relay works off the principle principle of electromagnetism. electromagnetism. Any ti me electrical current passes through a wire it creates an electromagnetic eld.

Creating Creatin g a Larger Electromag Electromagnetic netic Field •   Looping a wire wire around a metal metal core creates creates a much much larger  magnetic eld.

PRACTICAL AUTOMOTIVE ELECTRO ELECTRONICS NICS

 

CHAPTER 1

The relay uses this principle of looped wire to create a magnetic eld that will pull the relay switch either open or  closed.  closed. The real advantage of using a relay is you can use a very small switch and wire, which can only handle up to 0.2 Amps control a motor that handles 10 Amps. The switch in  the relay is large enough to handle the motor current.

This is a shielded wire most commonly used with oxygen sensors and knock sensors. If you were to cut open the wire you would see the shielding mesh around the inner wire. This shielding, shielding, which grounds grounds to the battery, acts to conduct conduct magnetic elds away from the inner wire. Relays, motors, etc., create magnetic elds that could induce induce a voltage into the (example:02 or oxygen) sensor wire giving the EFI computer a false signal. When some exterior force penetrates the wire shielding of the 02 sensor, the computer will receive a false signal. This is typically in the form of noise.

PRACTICAL PRACTICA L AUTOMOTIVE AUTOMOTIVE ELECTRONICS ELECTRONICS

11

 

12

SYMBOLS, COMPONENTS AND WIRE CONNECTIONS

Additional Electronic Symbols

Battery Stores chemical energy

and converts it to DC amperage for power to the vehicles electrical system.

Diode Made of two different semiconductor materials. It allows amperage to ow in one direction only.

Single Filament Headlight This is a one element  bulb since it only has one coil.

Capacitor 

Cigarette Lighter 

Temporarily stores an

Uses a heating coil to

electrical charge. If it has a direct ground it is typically called a condenser.

ignite cigarette paper material.

Zener Diode Used mainly as a voltage regulation device. It typically typica lly is connected to a circuit in reverse.

Distributor  Applies high voltage to each spark plug.

Double Filament Headlight One coil is typically used for high beam and other  for low beam.

Horn It creates an audible noise when electrical amperage is applied to it.

PRACTICAL AUTOMOTIVE ELECTRONI ELECTRONICS CS

 

13

CHAPTER 1

Light

Ignition Coil

Operational Opera tional Amplifer  Amplifer 

Uses low voltage DC

Amperage passes through

Amplies like a transistor 

amperage and converts it to high voltage for ring of the spark plugs.

it' s element causes causes heat and this creates light.

 but in addition it can have an additional input to control the amount of  amplication.

LED (Light  Emitting

Diode) When amperage ows through the diode in the forward bias direction it  produces light.

Analog meter 

Resistor  Has a xed resistance and is used in a circuit to reduce voltage to a specic value.

Tapped Resistor 

When amperage ows through it a magnetic coil is activated causing a needle to move.

By using the different tapped wires it can supply differentt xed resistor  differen values to a circuit.

Digital Meter  Amperage ow activates LED' s providing providing a digital display.

Variable Resistor  By adjusting it mechanically it can vary the resistance value between it' s lowest and highest highest resistor value. Also known as a rheostat.

PRACTICAL PRACTICA L AUTOMOTIVE AUTOMOTIVE ELECTRONICS ELECTRONICS

 

14

SYMBOLS, COMPONENTS AND WIRE CONNECTIONS

Analog Sensor 

Sensor (Thermistor)

Not Gate

The resistor' resistor' s resistance

Electromechanical switch

This circuit reverses

is affected porportionally  by changes in temperature.

inside is activated (pulsed) by external components. This creates a signal that can be ap plied to other systems.

whatever the input is. If  the input is 1 the output will be 0 and vise versa.

Solenoid

Short Pin

Used to move an interal  plunger of some sort. It creates an electromagnetic eld when power is applied to it.

Typically used within a  junction block. It will  provide an unbroken unbroken connection.

Double Throw Switch

 

Uses one switch or the other to apply power.

Transistor  Made up of semiconductor material, it acts similar to an electronic switch or relay.

Ignition Switch    

 

Wiper Park Switch

Controls the ignition sys-   tern and various other    systems by use of an ex  ternal key.  

Parks the wiper blades at the bottom of the windshield when the wiper  switch is turned to the off   position.

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

CHAPTER 1

Chapter 1 Quiz

1) a. What pins, shown above, are connected in the Dimmer SW Low Beam Mode?  b.  How many pin connections are there in the Dimmer SW Flash Mode? Identify the ones, used in this circuit only, by  pin number. c. How many pin connections are there in the Light Control SW Headlight Mode? Identify them by pin number.

Connector 

2) a. The connector pin number sequence increases in number  from left to right. What is the pin number in location x?  b.  Based on the direction of increasing numbers, is the connector a male or female connector?

c. From the information shown which  connector,  pin 10, would you back probe to check for power going all the way through the connector?

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CHAPTER 1

3)

a.  Wire A connects to which pin number on the Defogger  Relay?

 b.  Wire B connects to which pin number?

4)   The above illustration shows checking the continuity through the switch (to ground) ground) on a manual transmission transmission vehicle. vehicle. What pin number and connector on an automatic transmission vehicle would you check to do the same thing?

5)   a. When power is applied to pin 4 does the relay relay switch be-

tween 1 and 3 open, breaking the connection, or close it?  b. What type of relay is this?

PRACTICAL PRACTICA L AUTOMOTIVE AUTOMOTIVE ELECTRONICS ELECTRONICS

 

Chapter 2 VOLTAGE DIVIDER CIRCUITS 

Potentiometers and Rheostats These are variable resistance resistance devices used to vary the amount of amperage or voltage for a circuit.

Rheostats

Rheostat 

Rheostats have only two terminals Rheostats terminals connected to them. The terminals are in series with the load and the voltage source. The rheostat, when adjusted, varies the amperage in the circuit. A rheostat is a variable resistor. It has a mechanism that controls the amount of resistance resistance in the circuit. The artwork (below) shows a likeness to how a rheostat might work. Pushing the control control mechanism increases the internal resistance from 10 to 20 ohms.

Simulated Rheostat 

Increasing the resistance decreases the amperage in the circuit. In actuality the internal resistance can vary over many more than one resistor value. The minimum and maximum ohm resistor range is usually stamped on the rheostat housing.

Control  (Push to Increase Resistance)

 

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VOLTAGE DIVIDER CIRCUITS

Example: A 10-40 ohm rheostat can vary the resistance from Example: 10 to 11, 12, 13 ohms and all the way up to 40 ohms.

Constant Volta Voltage ge

Increasing Resistanc Increasing Resistance e Decreases Amperage.

The voltage difference difference across a rheostat rheostat does not change if  it' s the only resistance in the circuit, regardless regardless of its control setting. Moving the control setting to 30 ohms does decrease the total circuit amperage. A circuit with a rheostat and a resistor in series creates a voltage difference between the two.

 Adding an add  Adding addition itional  al  Resistor changes the Voltage.

Both the amperage and voltage vary in this circuit.

PRACTICAL AUTOMOTIVE ELECTRO ELECTRONICS NICS

 

CHAPTER 2

Fuel Injection Water  Temperature Sensor 

The water temperature sensor, used in the fuel injection circuit, acts similar to a rheostat. The resistance of the R2 sensor varies according to its tem perature. This varying resistance changes the voltage drop measurement at THW. The ECU then adjusts the fuel to the engine based on the voltage measured. In this example both voltage and amperage change as the resistance at R2 changes. Since this is an extremely low am perage circuit, varying the amperage is not a concern.

Potentiometers

A potentiometer acts differently from a rheostat since it contains three leads instead of two. The third lead is the output for the potentiometer and acts as a voltage drop like resistors in series.

Potentiometers have three terminal connected to them. The two outer terminals (1 and 3) connect across the voltage source. The inner terminal (2) vary the voltage and deliver it to the output source.

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VOLTAGE DIVIDER CIRCUITS

The output voltage, which is 6 volts in this example, is then applied to some external source.

Example A

Turning the control knob on the potentiometer changes both resistor values and in this example we have increased the output to 8 volts.

Example B

 Notice between example A and B that the amperage of the circuit did not change. The external 8 volt circuit cannot draw on any more than a 2 amp supply as well. So in this case you would not hook it up to a device that required 8 volts at 3 amps! It would not be enough power for the circuit. Vane air ow meters use a potentiometer to control the monitoring voltage to the fuel injection computer. As you can see the varying potentiometer control needle sends a varying voltage to the computer via the input terminal.

PRACTICAL AUTOMOTIVE ELECTRONI ELECTRONICS CS

 

CHAPTER 2

The advantages of using the potentiometer are: 1)  A second resistor is not needed in the circuit to create a voltage drop.

Voltage Drops divide

2) The amperage is minimized to a certain value thereby keeping the output circuit from drawing maximum battery amperage should it become grounded.

up the total Voltage

Voltage Drops Any time there is more than one load or resistance in a circuit there will be a division of voltage. Each resistance in the circuit circu it will consume consume its share of the total voltage applied. Each resistor with a value of 2 ohms each will drop 1/2 of  the total circuit voltage. The voltage remains the same no matter what sizes the resistor values are, just as long as they are equal in value. If we were to add one more resistor to the circuit our voltage division would look like as follows: See how the sums of the individual voltage drops add up to equal the source voltage of 12 volts.

RULE: If all resistors are equal in size, the voltage drop across each resistor is equal to the total voltage divided by the number of resistors in series.

Unequal resistor sizes cause a variation in the voltage drop across the circuit.

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VOLTAGE DIVIDER CIRCUITS

A mathematical rule applies here. It is: The total voltage drop in the circuit has to equal the total supply voltage to the circuit. A key point to remember is that voltage volta ge drops do not occur until power travels through the circuit. Measuring voltage drops are very helpful in diagnosing problems in a circuit if you know what the voltages should be. The light above should have the full 12 volts applied to it but instead we see only 10 volts. This means 2 volts are missing due to a problem elsewhere in the circuit. Measuring across the switch shows 2 volts and this is too high a resistance for this circuit. It now has become a voltage divider circuit. The light becomes one resistance and the switch becomes the other resistance.

Capacitors A capacitor stores electrical energy. It consists of 2 conductor   plates that are not touching. A space separates the plates. In some cases a non-conducting material called dielectric is used. When we connect a battery to a capacitor, the circuit acts like a complete circuit for a short time. Electrical current ows through the circuit until the capacitor' capacitor' s storage voltage equals that of the battery. The capacitor retains its storage capacity after we disconnect it from the battery. Note: it' s important to stress that a ca pacitor cannot produce electrical energy but can only store it temporarily. You measure capacitors in Farads. One Farad is equal to one coulomb of charge with a one volt potential difference difference placed across it. The more farads a capacitor has the longer it will discharge at a given voltage. Most automotive circuits use much smaller quantities. quantities. You will nd microfarads, microfarads, and even the smaller picofarads, in these circuits.

Charge when connected to battery 

Charge Charg e remain remains s when battey is removed 

PRACTICAL AUTOMOTIVE ELECTRONI ELECTRONICS CS

 

CHAPTER 2

Three things affect the size of a capacitor. 1)  The area of the plates 2)  The spacing between the plates

Ceramic Capacitor 

3)  The dielectric material used

A bigger capacitor has more plate area. Sometimes you will see a smaller capacitor with more capacitance. The smaller  capacitor uses a different dielectric material. For example an oil capacitor has 5 times more storage capability than air. A ceramic dielectric can have as much as 1200 times more storage than air!

Paper Capacitor 

Electrolytic capacitors Electrolytic capacitors are unique in that they must have a specic polarity for them to work properly. (CAUTION: USE PROPER POLARITY. IF YOU CONNECT AN ELECTROLYTIC CAPACITOR WITH ITS POLARITY REVERSED, I N SOME AC CIRCUITS, IT COULD EXPLODE!) To create the capacitor capacitor the manufacture manufacture uses two aluminum aluminum

Electrolytic Capacitor 

Symbol 

sheets and one saturated paper to separate them. They apply a DC voltage to the saturated paper causing a thin oxide layer  to form on one of the aluminum sheets. This thin layer creates large, low voltage, capacitance capability. Applying a higher rated voltage than the capacitor is capable Applying capable of handling to the circuit could break down the insulating  paper layer and destroy the capacitor.

How to test a Capacitor  A simple way to test a capacitor is with the use of a DVOM. Disconnect Disconn ect the power from the circuit. Holding the insulated insulated  portion of a screwdriver, use the metal blade to short the ca pacitor leads to each other. (CAUTION: DO NOT TOUCH BOTH CAPACITOR LEADS PRIOR TO DISCHARGING THE CAPACITOR. IT MAY HAVE A HIGH VOLTAGE CHARGE EVEN WITH THE POWER OFF). Disconnect one lead from the circuit and use the ohmmeter to check for  continuity through the capacitor. The ohmmeter may show a reading temporarily. This is normal as the capacitor is being charged up. A constant zero reading readi ng with no change over time indicates the capacitor capacitor is shorted therefore needing to be replaced. Set your VOM to Diode Check and hook the meter up to both leads of the capacitor observing the correct polarity. Keep the connection for some time (your using your meter to

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VOLTAGE DIVIDER CIRCUITS

charge up the capacitor). Disconnect the meter from the ca pacitor and switch to volts. Measure the voltage across the capacitor. It will show close to the voltage shown on Diode Check Chec k (my meter uses 3 volts). volts). A zero reading reading on the voltmeter indicates a shorted or leaking capacitor.  Diode check is much better than using the standard ohmmeter setting  since it applies a higher voltage to the circuit.  Note: capacitors, like batteries, do not hold their charge forever. There will be some internal leakage through the capacitor over time.

Old Style Gauges Years ago, I noticed my 1963 Dodge Dart had more gas  after  rst driving a few miles? Most basic instrument gauges  are of  the bimetal resistance type and it takes a while for the gauge to warm up. This may seem like a disadvantage but in actuality any quick change in fuel level, like hitting a bump in the road, does not affect the fuel reading.

The fuel gauge element, being made from two different metals called a bimetal element, bends proportionally to the amount of heat applied applied to it. Applying more current current to the element creates more heat. This increased heat causes the gas needle to move further.

Fuel Gauge Bimetal Element  Fixed Side

Fuel Gage

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

CHAPTER 2

A sliding resistor in the fuel tank controls the amount of current that affects specic deection of the fuel level needle.

Fuel Tank  Sending Unit 

Terminall to Termina Fuel Gauge

The battery having a base voltage of 12 volts increases to 14 volts after the vehicle vehicle starts charging. The system system needs a stable supply voltage voltage to keep the gauge needle from moving after the battery starts charging. Adding a voltage regulator to the system maintains this constant gauge reading. Typically the EWD does not show the gauge regulator being combined with the fuel gauge. You can determine if the gauge has a built in regulator by nding how many wires connect to it. If it has three wires going to it then it has a regulator regulat or built in.

Combined Volta Voltage ge Regulator and Fuel  Gauge

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VOLTAGE DIVIDER CIRCUITS

The voltage regulator works off the same principle as the Fuel Gauge. It has a bimetal element and when electrical current runs through it opens to break the circuit. The regulator cools down and reconnects. The gauge output typically is a much lower voltage than battery voltage. Usually this voltage is approximately 7 volts.

Typically the temperature gauge also uses the fuel gauges regulator for its circuit. In this case four wires connect to the fuel gauge unit. The regulator output wire connects to both the fuel and temperature gauge. Sometimes the fuel and water temperature Sometimes temperature circuit will have their own built in regulator unit. In this case each gauge will have three wires connect to it.

Note: Modern gauges use a solid state circuitt design which circui gives greater accurac accuracy  y  and durabil durability  ity .

One way to check either gauge is to disconnect the sender  and see if the gauge reads at one extreme side of the indicator (typically (typically empty for fuel or cold for temperature). temperature). Then replace repla ce the sender with a comparable comparable resistance resistance value (Some manufacture manufa cturers rs suggest a 3.4 watt light bulb). The gauge should now move to the opposite extreme side. You can sometimes check the regulator at point C for a uctuating voltage, roughly 4 volts. If the regulator or the fuel gauge is bad then you should replace the fuel gauge.

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

CHAPTER 2

Chapter 2 Quiz

1)

A 10-40 ohm rheostat' rheostat' s resistance resistance value is decreased decreased from 40 ohms down to 10 ohms. Is there any change to the amperage in the circuit?

2)   A 5 ohm resistor resistor is connecte connected d in series series with a 5 ohm rheorheostat. What is the total resistance in the circuit? 3)   When a resistor resistor is connecte connected d in series with a rheostat rheostat what

happens to the voltage measured at the rheostat compared to the source (battery) (battery) voltage? voltage? 4)   Complete the following following sentence: sentence: If you add add up all all the voltage drops in a circuit they will equal

5)   The abov above e circuit circuit has has 3 equal equal resistance resistancess in it. What What is the the

voltage drop across each resistor? circuit has the switch switch open open (no connection) connection).. 6)   The same above circuit What is the voltage drop across each resistor? resistor?

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CHAPTER 2

7)

a.  The voltage drop measured across the switch with it closed measures volts. How many should be measured at the light then? Will2the light glow dim volts or bright?

 b. What will be the voltage drop across the switch be if it is in the open position?

8)

12V

switch

2 Amps

2 Amps

2 Amps a.  What is the voltage drop across each resistor shown above?

 b.  What is the total amperage owing through the switch when it is closed?

PRACTICAL PRACTICA L AUTOMOTIVE AUTOMOTIVE ELECTRONICS ELECTRONICS

 

Chapter 3  ALTERNA  AL TERNATING TING SIGNALS AND SENSORS 

ALTERNATING SIGNALS Look at the drawing below. You can see four consecutive  pictures of the meter' s voltage level. If you were to use a faster camera there would be more dots. So many so that you would see a line forming.  Notice that the line: li ne: (a) starts at zero; (b) ( b) increases to 30 volts; (c) decreases to zero; (d) decreases to -30 volts; (e) returns to zero. This process from point (a) to point (e) is one complete cycle.

 A Simple Simple AC Gen Gen-erator Armature Rotated at Constant  Speed 

 

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 ALTERNATING  ALTERNATIN G SIGNALS AND SENSORS

This is a typical alternating voltage or better known as AC voltage. voltag e. The primary primary factors that affect affect the strength strength of the voltage created are: 1)  The strength of the magnetic eld. 2)  The speed of the conductor movement. 3)   The length of the conductor in the eld. 4)  The angle at which the conductor cuts the eld.

Looking at g. 1, on the previous page, a conductor cutting the eld at right angles yields the greatest amount of voltage. A conductor cutting the eld at a parallel angle yields zero voltage. Thus the strength of the voltage is continuously changing changin g through out the cycle.

 Alternating or AC   Alternating Signal 

one cycle Every cycle of an AC voltage has one positive and one negative peak. Together they make up one cycle. If one cycle happened in one second you would call the signal one cycle  per second or one hertz. Hertz is a term for frequency.  Notice as the numbers of cycles increase in one second' s ti me so does the frequency. The voltage refers to the size of  the peak. In automotive systems the positive peak is the most useful as most circuits do not use negative voltages. When using an AC signal, Automotive Electrical Engineers design the circuit to ignore the negative peak or convert it to a positive peak  through additional circuitry. Since AC is always changing, AC voltage and amperage are not equal to DC voltage or  amperage.

The Voltage refers to the size of one peak 

PRACTICAL PRACTICA L AUTOMOTIVE AUTOMOTIVE ELECTRONICS ELECTRONICS

 

CHAPTER 3

Let' s say you wanted wanted to compare AC voltages voltages to DC voltvoltages. You will have to convert the negative peak to a positive  peak using a diode rectication circuit. Since AC is always changing, one volt AC peak voltage is not equal to one volt DC voltage. One volt AC averages out to equal about 0.707 DC volts. This is the RMS value of an AC peak. You have to have more AC voltage to equal the same amount in DC voltage. How does knowing knowing the differenc difference e between AC and DC signals affect affect you? You can' t use a DC meter to measure an AC signal. You need an AC meter to measure the RMS signal. Since it is an RMS voltage the actual peak voltage will be higher. To get the peak voltage multiply your RMS meter voltage times 1.41. Then remember that the meter only reads the  positive signal and that there is a negative signal of the same size. The total peak to peak AC signal would be 2 times the AC peak signal! A much easier way to determine what is happening with an AC signal is to connect an oscilloscope to it and see the signal. One volt peak AC volts on the oscilloscope will read .707 volts on an AC meter. What is more important than reading the voltage is you can measure and see the frequency with an oscilloscope oscilloscope.. Seeing the frequency is a big advantage. You can see if the signal is erratic where where an AC meter wouldn' t. Another disadvantage of the AC meter is that it can only read sine waves accurately (waves that look like perfect half circles). The meter reads any other wave improperly. Most automotive AC circuits do not use a perfect sine wave. This reduces your AC meter to nothing more than a basic "Go, No Go" test for a signal. Automotive signals typically look similar to an AC sine wave  but they are not. Look at the difference between the sine wave and a distributor output signal. The distributor output signal is not a perfect sine wave.

Typical Distributor  Signal 

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 ALTERNATING SIGNALS AND SENSORS

OPTICAL SENSORS Optical sensors use the light emitting diode and the photo transistor in conjunction to convert the breaking of a light  beam signal into an electrical signal the computer can read. The manufacturer designs the output voltage from this sensor  to be close to 2.0 volts (though they can set it as low as 0.8 volts or as high as 2.4 volts). The advantage of using this system is that the maximum voltage output will remain the same regardless regardless of the speed of the wheel.

Typical examples of where the automobile uses this sensor is, crankshaft position sensors, speed sensors, and some air ow meters.

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

CHAPTER 3

An example of use within an airow meter would be on the Toyota Turbo Supra that uses the karman vortex airow meter.

Toyota Karman Vortex   Airow meter 

This meter has a vortex generator (air current) that oscillates a mirror. Light intermittently bounces off the mirror onto a  photo transistor. The photo transistor sends a square wave signal to the computer.

Increasing the airow past the mirror cause the oscillations of  the mirror to increase. The airow meter sends an increased square wave frequency to the computer. The computer then adjusts fuel output based on the increased frequency.

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 ALTERNATING  ALTERNATIN G SIGNALS AND SENSORS

Use an oscilloscope to test this type of frequency signal. Connect the oscilloscope to terminal KS and ground as shown in the illustration. You could also use a frequency me-

ter to test this circuit. If after determining that there is no KS signal, you should check power at VCC and ground at E2  before replacing the airow meter. If you replace the airow meter rst, without checking for  correct voltage at VCC, you could damage the new airow meter (assuming VCC output voltage is much higher than 5V in this case). Get in the habit of asking yourself WHY DID THE AIRFLOW METER METER FAIL? Let' Let'ss say the computer is malfunctioning. It sends a 15 volt signal to VCC instead of  the correct 5 volt signal. Over a short time, the meter will fail again and you will have an unhappy customer back.

It' s important to get as much info informatio rmation n about the car that you can. One of my previous students had a Toyota Camry that kept destroying its EFI computer. After the 3rd com puter, The student asked the customer when he rst noticed the problem. It was after another garage replaced his blown engine with a used engine. The student later determined the garage had installed a 1986 Camry engine in a 1987 car. Toyota changed changed the injector resistance in Camry' s from 2 ohms to 31 ohms in 1987. The 1987 car was using 1986 in jectors with 2 ohms of resistance. This caused a lot more current to go through the main drive transistor. The computer  would last about 2 weeks before its main transistor would  break down and ruin the computer unit.

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

CHAPTER 3

As noted earlier, you cannot accurately read a square wave with a voltmeter. To determine if the signal is breaking down, connect an oscilloscope to it and check its wave form  pattern.

The other alternative is to check the signal to see if it has any voltage by using an AC meter. This is inaccurate but at least gives you some indication whether it is outputting any kind of signal therefore indicating that it is working. If the system is having problems intermittently the oscilloscope scop e may be the only accurate accurate way to test for this. AC and DC meters take an average; the system may show good constant voltage yet if you were to check the same signal on an oscilloscope it would show you exactly what is happening at that moment. The example example shows an AC meter reading the correct correct average RMS voltage even though the signal is faulty.

Optical Sensor Disadvantage The disadvantage of using external optical sensors is if their  shielding breaks down they can get dirt and oil on them. The LED will not trigger the photo transistor and the system will stop working.

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 ALTERNATING  ALTERNATIN G SIGNALS AND SENSORS

MAGNETIC RELUCTANCE POSITION SENSOR

Only Portion of Sensor  Disk is Shown

When a magnetic eld moves across a wire it conducts a voltage potential in that wire. In other words the magnetic ux (or eld) changes in strength as it moves across the wire inducing a voltage in the wire. Since metal conducts ux some thousand times better than air, we can change the eld in a stationary wire by moving a metal pole piece through the eld changing its ux. This induces a voltage potential. The voltage volt age is AC and looks very very close to a sine wave. wave.

Modern Crankshaft Cranks haft and  Camshaft  Position sensors work  off a similar   principle

This signal will increase in amplitude (size) and frequency (number of oscillations per second) as the pole piece rotates faster. Many vehicle ignition distributors use this circuit. One can tap into the circuit circuit with an AC voltmeter voltmeter crank the engine and If one sees voltage this indicates the sensor is working. Tapping into the circuit before signal processing will give you a typical sine looking wave on an oscilloscope. If  the sensor has a built in signal processing circuit, you may only see a square wave output (since the only available leads are after signal processing). Other systems have the signal  processor built into the computer.

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

CHAPTER 3

KNOCK SENSORS The knock sensor is a voltage generating device. It requires no external battery. It uses a piezoelectric crystal that when vibrated at a certain frequency will create a voltage. This is the typical symbol for a knock sensor. The automotive manufacturer mounts the knock sensor on the engine engin e cylinder block. An engine knock creates a vibrating vibrating frequency of 7,000 hz. When the sensor recognizes this frequency it presses on its inner crystal. This pressure on the crystal creates a voltage. The engine computer senses the increase in voltage and retards the ignition timing to eliminate the knock. This is a typical signal for a knock sensor.

Using an oscilloscope is the only way to monitor this fast varying signal. Most computer systems will monitor the sensor and wiring for an open or short. The computer will generate a diagnostic code if it detects either. One problem that occurs if the shielded wire gets a pin hole in the braided shield itself. Extraneous electromagnetic elds from other electrical systems can induce a voltage into the sensor wire causing the computer to trigger a knock sensor  code. You cannot repair shielded wire; you must replace it. One can buy 0.9 mm coaxial speaker wire from an electrical  parts store and use that in place of factory wire. Make sure the shielding portion of the wire itself grounds to the engine  block. Otherwise you will have to replace the whole harness  just to get the one wire!

One way to check the sensor and wiring is to check the signal as it enters the computer. One can tap on the block or  sometimes race the engine and if you see a signal on the oscilloscope assume the knock sensor and wiring are O.K.

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 ALTERNATING  ALTERNATIN G SIGNALS AND SENSORS

Both MAP and MAF  sensors produce an electrical signal that  is input to the EFI  computer to calculate the amount of air being  drawn into the engine.

Wheatstone Bridge Circuit 

Note: Bellows is not  shown. Strain Gauge Sensor would be connected to the side of  the bellows.

Graph of changing  Map Sensor Output  Voltage based on  pressure  pres sure at the bellows.

MAP SENSORS The map sensor uses a strain gage that connects to a sealed low pressure pressure bellows. bellows. As the bellows bellows expands and contracts, contracts,  based on the pressure applied to it, the strain gage resistance varies. The whetstone bridge cancels effects of temperature affecting a change in resistance in the circuit. Then the signal goes in to the differential amplier and on to the computer.

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

CHAPTER 3

OXYGEN SENSORS Measuring the amount of oxygen in the exhaust gives an indirect measurement of air/fuel ratio. Therefore the electronic fuel injection computer can adjust the ratio to maintain stoichiometric (14.7 lb. of fuel to 1 lb. of air). There are two different types of sensors. The Zirconia Oxide EGO Sensor that is the most common and the Titania Oxide Sensor.

ZIRCONIA ZIRCO NIA OXIDE SENSO SENSORS RS The zirconia oxide sensor creates its own voltage based on the amount of oxygen in the exhaust system. In a sense it is a  battery and creates a varying DC voltage. If the exhaust is running very rich and lacks oxygen the 02 sensor will output its highest voltage (typically 1 volt). The computer then leans out the mixture adding more oxygen causing the voltage to drop to zero.

One check for proper operation of the 02 sensor and system is to see a varying voltage needle at above idle speeds in the  proximity of 2000 RPM. The 02 sensor will not properly operate until it has reached a temperature of 750 degrees Fahrenheit. Therefore warm up the engine before making this test. If the needle does not uctuate it does not necessarily indicate a faulty 02 sensor. Let' s say you have two leaky fuel injectors. The 02 sensor will trigger the computer to lean the system out but if the leak is too much for the computer to handle the 02 sensor will indicate a constant 1 volt signal. Therefore it is necessary to see if the needle will go to zero volts by introducing a vacuum leak into the system (try un plugging If the the02 needle now moves zero voltsvacuum you canhoses). assume sensor is OK andtoward your   problem lies elsewhere. Something else in the system is causing causi ng the 02 sensor to stay rich (two leaky leaky injectors in this example) examp le) and the 02 sensor can' t compensate compensate for this.

Voltmeter reading 02  Sensor works for Titania sensor only 

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 ALTERNATING SIGNALS AND SENSORS

TITANIA TIT ANIA OXIDE SENS SENSORS ORS The Titania Oxide Sensor does not create its own voltage rather the fuel injection computer applies power and ground to it. You might think of the sensor as if it were an oxygen resistor. It creates a variable resistance depending on the amount of oxygen in the exhaust system. Therefore it acts as a voltage divider circuit varying the voltage at the xed resistor RX. The voltage drop across the oxygen sensor increases creas es thus causing causing the voltage drop across RX to decrease.

Still the voltage across the sensor acts very similar to the voltage signal of a Zirconia Sensor. The important thing to note about this sensor is that it does not generate its own voltage. The computer applies power and ground to the circuit in order for it to operate. The varying resistance of the circuit creates a corresponding voltage that is directly proportional to the oxygen partial pressure and temperature.

PRACTICAL AUTOMOTIVE ELECTRONI ELECTRONICS CS

 

CHAPTER 3

Chapter 3 Quiz

speed sensor signal, signal, at at 15 mph, on the the 1)   When measuring the speed oscilloscope above, you determine that in one seconds time there are 3 cycles. What is the frequency? 2)   Measuring the above speed sensors signal using an AC meter  measuring RMS voltage you measure 1 Volt RMS. How much total voltage (Peak Positive to Peak Negative) would this be if you were reading it on the above oscilloscope?

electronic fuel injection injection vehicle which uses a magnetic 3)   An electronic reluctance position sensor will not not start. A mechanic uses an AC RMS meter to check to see if the sensor is outputting any voltage. The meter does read a voltage while the engine is  being cranked. Does this verify that the sensor is working  perfectly?

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CHAPTER 3

4)

A vehicle equipped with a knock sensor exhibits heavy detonation natio n (pinging) (pinging) under acceleratio acceleration n conditions conditions.. A technician technician hooks up an oscilloscope at point Z above and increases the vehicle' vehi cle' s engine RPM. RPM. A zero sign signal al is indicated indicated on the scope. Should the technician replace the computer? fuel injected injected vehicle vehicle equippe equipped d with an 02 Sensor con5)   A fuel stantly stalls at idle. A technician hooks a voltmeter voltmeter across the 02 Sensor and gets a steady reading of 0.1 volts when running. He hooks a variable resistor in series with the water  temp sensor and fools the computer into making the air/fuel mixture more rich. The voltmeter now indicates 0.9 volts and is steady. Should the 02 sensor be replaced?

PRACTICAL AUTOMOTIVE ELECTRON ELECTRONICS ICS

 

Chapter 4 SEMICONDUCTORS 

A semiconductor is a substance whose electric conductivity is intermediate between that of a metal and an insulator. What is more important is how do semiconductors differ from  typical components; and what components contain semiconductor  material? The two most common common components components you' ll  work  with are diodes and transistors.

DIODES This is the symbol for a simple diode. Using conventional current ow theory amperage always ows in the direction of  the arrow. A good rule to remember is the arrow always  points to the negative lead. When current ows through the circuit in this manner the diode is  forward biased. When we  reverse bias  the diode, or hook it in the opposite manner the circuit no longer conducts amperage.

The circuit acts effectively as a switch that is open.

 

44

SEMICONDUCTORS

Checking Diodes The Digital Volt/Ohmmeter uses very low internal internal voltage to test a circuit in ohms made; thus it will not effectively check  a diode. Your meter should have a diode check mode specically for checking diodes. This mode increases the meters test voltage and it allows you to check the diode directly.

VOM Meters Diode Check Mode uses more voltage

Make sure you disconnect the diode from the circuit before testing it.

Check the diode with the meter in diode check. The diode should have a reading in one direction only (one high and one low reading). If the meter reading is high in both directions the diode is bad (open). The diode acts just as a wire that has broke into two parts. In diode check the meter does not measure ohms rather it measures volts. This is the actual amount of voltage that the circuit uses up just to "turn on" the diode. In a circuit the voltage would look like this.

Diode consumes 0.6V  regardless of Input  Voltage setting 

Since the diode uses 0.6 volts to turn it on, only 11.4 volts remain for the resistor to use.

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One of the unique properties of the diode, unlike the resistor, is its voltage remains the same; even if we increase the sup ply voltage.

Diode voltage drop remains at 0.6V 

The diode will only allow so much power to go through it  before it breaks down. Electronic Designers match the diode to balance the circuit power requirements. Power equals  amps multiplied by volts and if either there is too much volt- age or amperage in the circuit the diode will burn up. Keep this in mind when a semiconductor device malfunctions for know apparent apparent reason. Ask yoursel yourselff what could cause the circuit to have an increase in amperage or voltage over its designed rating. The manufacturer adds a diode in some semiconductor circuits to protect them from intermittent voltage spikes. They are know as Despiking Diodes.

Turning on or off a relay has the potential for creating a voltage spike in the circuit its in. When this occurs magnetic lines of force create a temporary voltage that is much higher  then the source voltage. They can be as high as 200 to 400 volts in a typical relay. This voltage is so much higher than the battery that is can  power itself through most circuits forwards or backwards. Transistors are especially susceptible to this high voltage that would cause them to "blow."

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SEMICONDUCTORS

Despiking Diodes

Automotive Electrical Electrical Wiring Diagrams Diagrams (EWD' s) tend to simplify the circuits to the point where they will sometimes not show a despiking diode. Designers attach them in the circuit (usually connected to a component) to protect the semiconductor device. If the diode fails and causes the com ponent to fail, replacing the component also replaces the faulty diode. Beware of despiking diodes that are elsewhere in the circuit  because replacing the failed component does not replace the cause of your problem, a faulty diode. These spikes are typically so quick you will not be able to detect them with a typical voltmeter. If you do try to test for a spike with a new component compone nt you risk ruining the component component as well. Also some spikes in the circuit are normal; relays produce them! The good news is that if the despiking diode is in the circuit  by itself the EWD will show it. Remember Remember to check for such diodes and test them before installing a new component.

Diode protec protects ts Trans Transistor  istor  from Relays High Voltage Spike

Spike Voltage goes through the Transistor and the Battery. It momentarily becomes it's own Voltage Battery and damages the Transistor.

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CHAPTER 4

ZENER DIODES If you take a regular diode and connect it to a circuit with reversee polarity revers polarity no current current will ow through the circuit. circuit. Remember that the arrow has to point toward the negative battery terminal for current to ow through the diode. Each diode has its own limited amperage capacity in the forward bias direction and voltage capacity in its reverse bias direction. direct ion. Therefore Therefore if we apply enough voltage voltage in the reverse reverse  bias direction eventually we' ll reach a peak where the diode will break down and start conducting current. Depending on the diode its reverse break down voltage can be anywhere from 40 to 1000 volts for example. Let say we have a relay circuit with no despiking components attached to it. We connect to it a diode with a maximum of  40 volts maximum revers reverse e breakdown voltage. The relay puts out a 100 volt spike toward the diode in the reverse bias direction. This will break down the diode ruining it and allow current to conduct through it in the opposite direction. Two ways to ruin a diode and exceed its power requirements are: 1)  Apply more amperage than the diode can handle in the forward bias direction. direction. 2) Apply more voltage than the diode can handle in the reverse bias direction.

Look at the symbol for the zener diode.  Notice the addition of the slanted tabs. Like a standard diode, all the rules apply to the zener diode as well. Yet  the  zener  diode works in the reverse bias direction at a much lower  break down voltage.  In fact it does not actually break down  because it is designed to work that way as long as you do not exceed its maximum reverse voltage. The zener diode typically operates backwards from a standard diode; the manufacturer manufacturer designs it this way. The unique characteristic of the zener is that even though the source voltage varies the voltage at the zener diode remains at a regulated or constant regulated constant voltage. This makes the zener diode circuit an ideal voltage regulator.

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SEMICONDUCTORS

For example, even though the source voltage varies (10 volts starting the car to 14 volts charging the battery) the voltage at the zener diode remains at a constant 5 volts.

Resistor R1 limits the current in the circuit to 49 mA allowing the diode to function as long  as this amperage is not exceeded.

A 5 volt power supply circuit (shown in Fig. A) outputting at VCC is very common in automotive vehicles. In actuality it  is nothing more than a zener diode circuit shown in Fig.   B.

The battery contains 12 volts and if we have 5 volts outputted at the zener diode what happened to the additional 7 volts? The resistor 111 created a 7 volt drop. If you start the vehicle the alternator increases the source voltage from 12 to 14 volts; yet the zener maintains a 5 volt output. Its semiconductor properties are that it takes 5 volts to  push through it and turn it on. When the source voltage increases to 14 volts the resistor RI drops the remaining voltage of 9 volts.

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What happens if the source voltage drops below the rated zener voltage? For example, lets say we have a 5 volt zener  circuit and the 12 volt battery voltage drops to 4 volts. Will the zener zener maintain a 5 volt output? It won' t because it takes 5 volts to turn on the zener. We only have 4 volts so that is what the zener will output.

RULE: ZENER DIODES DROP SOURCE VOLTAGE DOWN TO THEIR RATED VOLTAGE AS LONG AS THE SOURCE VOLTAGE IS HIGHER THAN THE RATED VOLTAGE. This is why it is always important to check you source voltage and ground rst before condemning condemning a circuit' s voltage regulator. If the ground has a high resistance it will drop the source voltage and the regulated voltage giving you a false impression that the regulator is faulty.

LIGHT EMITTING DIODES The manufacturer of Light Emitting Diodes adds properties  to their material so that they emit light when amperage passes through them. The symbol for the Light Emitting Diodes, LED'' s for short, LED short, uses arrows to indicate indicate light light emitting emitting from the diode.

One of the main advantage advantagess that LED' s over light bulbs is they have an unlimited life expectancy and they use very little power. The LED symbol may just have a circle around the diode symbol to indicate that it is an LED. The only bias that the LED will produce light is in the forward bias direction (the arrow in the symbol points to the negative). Adding the resistor R to the circuit limits the amperage through the circuit and thereby protecting it. Each LED has to operate in a specic amperage range.

The LED takes more forward voltage to turn it on than a standard diode. It takes approximately 1.5 to 2 volts in some applications. This means that you have to have more than 2 volts to power the LED. Then with that additional voltage you determine determine what resistor you' re to use to limit the amperage to that specied by the LED manufacturer. If the LED malfunctions prematurely check to see if the resistor in the circuit is maintaining it' s correct resistance value. value.

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SEMICONDUCTORS

TRANSISTORS Transistors are like diodes in that they contain the same semiconductor material as diodes. They also have an extra lead compared to diodes.

Transistor 

Diode

The illustration shows that if you connected only two of the three leads the transistor would work just like a diode. You would connect it similar to a diode with a forward bias connection This would allow power to ow through the circuit. One good biasing point here is that the arrow always points to the negative battery terminal if you want amperage to ow through the circuit.

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In a transistor the three leads have names to eliminate confusion in connecting them.

NPN  Transistor    Transistor 

Power ows into the B or Base lead and out the E or Emitter  lead.. This is also the trigger circuit lead circuit that turns on the transistor. If you reverse the power leads no current will ow and the transistor will stay turned off.

The main drive circuit is the C or Collector to Emitter Circuit. It carries most of the power. If you were going to turn on turn  on a small light this is the side of the circuit you would connect in series with the bulb.

The Entire Circuit would look like this: Note: Transistor  drawn differently  still works the same as above

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SEMICONDUCTORS

Transistors function a lot like relays

Transistors function a lot like relays. Both apply more power  to the light than the switch is able to carry. We have a small amperage in the base or relay coil controlling an output contact in the relay.

We call this amplication. We are taking a small power  source and making it bigger. In reality we are just taking a small power source and having it connect to a larger power  source in a way that it can control the larger power source. Then we connect the larger power source to the output circuit.

Switch is in the Input  Circuit and the Light  Bulb is in the Output  Circuit 

In most transistorized units you will see more than one transistor. The transistors connect in stages. A very small input amplies going through TR1. Then this signal amplies again going through TR2. This allows you to apply much more power to the output device. The initial trigger switch and wiring can be very small thereby reducing the costs of such items.

Transistor Amplication through Stages

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CHAPTER 4

The transistors have no moving parts in them unlike the relay contacts which over time eventually burn out. The small in put switch uses a very low amount of power so it will last a very long time. The other advantage of transistors is they are smalll and don' t take up much room. smal Knowing how transistors in circuits operate will make it easier for you to diagnosis the circuit when it malfunctions. In Automotive Fuel Injection Computers, for example, there are several transistors connected to one big output transistor  called a Driver Transistor. The Driver is in series with the fuel injectors and it controls them. You can tell it’s the Driver since it’s mounted to the case of the computer to dissipate heat due to the high current that ows through it. If an injector wire shorts to ground, it creates much too high of  amperage in the Driver Transistor. This high amperage will ruin the Driver Transistor yet leave the other transistors intact. Don' t bother trying to check the computers' computers' transistors; transistors; rather you should check to make sure all the resistances in the circuit are intact (in this example measure the injector  resistances). If the polarity is reversed the transistor will not work.

I mproper mproper Polarity 

If the base that should be positive contacts ground giving it a negative then the transistor will never turn on.

Shorted Base Circuit 

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SEMICONDUCTORS

Some transistor circuits will have a transistor with the arrow  pointing the opposite way. This is a different type of transistor but the arrow rule still applies.

PNP Transistor (arrow   points  point s to negative negative for   proper  prop er pola polarity) rity)

We apply a ground ground (negative (negative base voltage) with this transistransistor to turn it on. We applied power (positive base voltage) to the previous transistor to turn it on. Always look what direction the transistor transistor arrow points and you' ll be able to determine how it operates and what type of transistor it is.

The circuit shows the completed circuit using a ground through switch S1 to ground the base circuit and turn the light on. The reason for the resistor RI is to limit the amount of current owing through the circuit. If we were to bypass that resistor we may ruin the transistor. Limiting power through this circuit depends on the wattag wattage e capacity of the transistor and resistance value of the light

Resistor R1 protects transistor by limiting  the amount of current  owing through it.

 bulb. only one ohm and voltage sourceIfisthe 12light voltsbulb thensay it ishas capable of owing 12the amps or 12 amps times 12 volts that would equal 144 watts through the transistor. If the transistor say has a 10 watt capacity we are going to ruin it! What do you think would happen if we short a wire across the light bulb? Answer: too much amperage through the transistor would ruin it. Most transistors inside microprocessors are only capable of  owing only milliamps (0.001 amps or so) through their circuits therefore therefore it doesn' t take much to ruin the whole micro processor chip.

PHOTO TRANSISTORS Occasionally you will see a transistor in a circuit with the following symbol. This is a photo transistor. When a light shines on it the base turns on conducting current from the collector to the emitter. Manufacturers use this type of sensor in their optical circuits. Toyota has a steering sensor that uses photo diodes that shine on the photo transistor through a plate. The plate moves and  breaks the light beam thus indicating the speed and direction of the turning steering wheel.

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CHAPTER 4

Chapter 4 Quiz

1)

 

DIODE CHECK

The above diode was removed from the circuit and checked in both the forward and reverse reverse bias direction. direction. According According to the illustration is it good or bad?

2)

The above horn circuit works for only a short time. The horn switch circuit (combined with transistor) has to be replaced every month. The EWD shows a despiking diode in the horn relay. How could you test to see if that diode was functioning  properly (as you cannot remove it from inside it' s relay case without destroying it?)

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3)   A customer complains complains that he has to replace the semiconducsemiconduc-

tor module to his electronic ignition system every 3 months. He also has to put more water in his battery since this has  been occurring. Which would you check the system for, high amperage or high voltage?

 A

4)   Will the above above short cause cause the transistor transistor to burn out?

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Chapter 5 INTEGRATED CIRCUITS 

The integrated circuit chip, that is about the size of a dime, is a complete electronic circuit consisting of diodes, transistors, resistors and capacitors. The material used to create the component is the same material that manufacturers use to make transistors. One chip contains hundreds of transistors and has no solder connections. This makes the integrated circuit highly reliable and affordable. The disadvantage of integrated circuits is they cannot use much power. The heat created due to increased amperage through the chip would destroy it. Therefore the nal com ponent connected to an integrated circuit is a power transistor. The manufacturer connects it directly to a metal case to

dissipate the heat due to high amperage owing through it.

 

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CHAPTER 5

Integrated Circuit Controlling a Power Transistor 

There are several terminals on the chip for control. Currently, our interest is with power to the chip and how that power  gets to the power transistor. Pin 7 is power for the chip as pin 4 is grounding for that power. Pin 6 is the output of the  IC chip that drives the power transistor.

Operational Amplier  Operational with External Chip Not  Normally Shown

Take care when replacing these chips as it takes very little amperage to ruin them. Walking across a carpet creates static electricity. Then touching the chip could discharge that electrical charge charge destroying destroying the chip. Thus it' s a good idea to touch the case/chassis with both hands (grounding them) to discharge any built up electrical charge before installing the chip. You can' t rebuild an IC chip after it has failed therefo therefore re you must replace it. Typically you will not have access to another  chip rather you will replace the component that the chip belongs to. Different chips contain different circuits inside of them. An Automotive Electrical Wiring Diagram may only show the symbol and how the chip works with a specic circuit. Therefore it may not show all the chips' chips' connections. connections. This is an example example of what you don' t see in the EWD. You will see instead the inner symbol for diagnostic purposes. It would be confusing to show how the power directly connects to every IC chip. All you really have have to do is check for power  and ground to the main component that the IC chip is in.

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INTEGRATED INTEGRAT ED CIRCUITS

OPERATIONAL AMPLIFIERS Operational Ampliers, OP amps, typically amplify signals and can do it in many different ways; too many to go into depth in this manual. The most common amplication used in automotive applications is differential control. An external system inputs 2 differing signals into the OP amp and it compares them. If the signal voltages are equal the OP amp outputs a zero signal.

OP  AMP Typically 

used for Differential  Control  If the two input signals are of differing voltage the OP amp ampliess the output voltage to 12 volts. amplie

This in turn could drive a relay that controls an electric motor.

Electric Motor Runs until there is a difference in Input Voltages

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Some OP amps use amperage as an input signal and voltage for an output signal.

If Input Amperage of A and B are Both Zero or  the same then No Am plication  plic ation to Outpu Output  t 

Automatic Down Window Controls use OP amp circuits. This is not the exact circuit but the basic principle applies.

You operate the auto down button rst triggering the electric window motor to crank down the window. The OP amp compare com paress the amperag amperage e in circuit circuit B to that of circuit circuit A. The window motor continues to run since there is no difference in the 3 amp input input voltage voltage at A and B. Once the window is down the motor binds due to resistance and stops. This non-running of the motor increases the am perage to B since a non running motor creates less circuit resistance. You can see the amperage at B has now increased to 5 amps. This differing input amperage now applies the relay opening the contacts to the motor shutting it off.

 Automatic  Automati c Down Window Control in Off  Mode due to difference in Input Amperage

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LOGIC CIRCUITS In the wiring diagram you may see the symbol for the NOT gate. In logic a 1 is a high input and a 0 is a low input.

NOT GATE 

The truth table for the NOT gate is as follows.

NOT GATE TRUTH 

INPUT   OUTPUT   C  A

TABLE 

 If A is High (1) then C  is Low (0)

1

 

0

0

 

1

If the input on A is high then the output of C is low and vice versa.  connected to the opposite Sometimes you will see the circle the  circle connected end of the triangle. Both symbols represent the same NOT gate. Do not confuse the previously described described OP amp symbol with the logic circuit symbol shown above. The NOT gate always has only one lead attached to it. The circle attached to the triangle is a real key in determining that it is a logic circuit and not an OP amp.

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AND GATES Integrated circuits Integrated circuits also can contain logic circuits. circuits. A logic circuit has one to multiple inputs and one output. The output lead will be high or low depending on the voltage values ap plied to the input leads.

QUAD AND GATE  Integrated Circuit 

The above integrated integrated circuit circuit has 4 AND gates. When When you look at EWD' s you will not see the whole chip chip circuit as you see here. You will see possibly one of the AND gates only. This does not mean the integrated circuit is not there only that one section of it is being used. This circuit contains more complex connections. You only need to know the logic information for diagnostic purposes. Therefore these are all the connections you need to know about as long as you check for power and ground to the component this chip is in. Let' s take a look at how how logic works works for the AND gate. gate. First lets dene High and Low voltages.

Digital electronics can only read 0 and 1 volts. The logic gate will read any voltage below 1 volt as a 0. The logic gate will read any voltage above 1 volt as 1. For example the logic gate considers a 12 volt input reading as a 1 and a 0.2 volt reading as a 0.

Input Voltages on Left   AND Gate are equiva equiva-lent to Input Voltages on Right AND Gate

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INTEGRATED INTEGRAT ED CIRCUITS

An input of 0 volts on A and 0 volts on   B  we get an output of 0 volts on C. Still if we apply 1 volt on A and 0 volts on B we still get an output of 0 volts on C. We apply 1 volt to both A and B then we get an output voltage of 1 volt. This agrees with the truth table as you can see.

INPUT  AND GATE Truth Table

 A

OUTPUT B

C

0

 

0

 

0

0

 

1

 

0

1

 

0

1

 

1

0

1

We can now use logic logic to turn on a light. Apply Apply a 1 volt input input to both A and B of the AND gate and the light turns on.  Take the power away from A or  B and the light will turn off. Input' s A and B could be from a door switch, brake lights, Input' lights, etc. The actual voltage used is higher but the logic circuit reads a voltage higher than 1 volt as a 1 as you already know. We will now concern ourselves with 0 or 1 and not mention volts.

 Applic ation of an AND  Application GATE 

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Some logic circuits have 3 input leads. You will not see an extra column in most truth tables as I have shown here. Therefore you must use a little common sense in determining the logic pattern. You should determine determine that any where there are two zero' s on the input then three zero' s would also give you a zero outpu output. t. You should determine determine that any where there are two one' s on the input then three three one' s would also give you a one output. Any combination of 1 or 0 on the input will give you a 0 output. INPUT

3 Lead AND GATE  Truth Table

RULE 

 

These are Different  Gates due to the Symbol Change

 

OUTPUT

B

 

C

 

D

0

0

 

0

 

0

0

0

1

 

0

0

1

1

 

0

0

 

0

0

 

1

 

 A

 

1

 

0

1

 

1

1

 

1

 

0 1

Any change change to the symbol symbol (besides (besides the numbe numberr of input leads) changes changes the AND gate to another another type of gate and you use a different truth table to determine its logic.

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INTEGRATED INTEGRATE D CIRCUITS

Let' s combine our knowledge knowledge of the NOT and AND gates in a circuit.

It will help to write 1 or 0 at both sides of the logic gate as you analyze power and ground going to it. Looking at the seat belt switch you can see that it is in the closed position. This will ground the NOT gate and so you should put a 0 down at point A. Looking at the NOT gate truth table with a 0 input will yield a 1 output.

NOT and AND GATE  COMB CO MBINE INED D LOGIC  LOGIC  CIRCUIT 

A question that may come to your mind is how can a 0 voltage input at the NOT gate cause a 1 volt output when this is the only connection in the system? Remember the EWD diagram does not show all the connections going to the NOT gate; there is power applied to it. The 1 at the output of the NOT gate applies to one of the inputs of the AND gate. Power through the ignition fuse to the other input of the AND gate applies a 1 output (Look   back at the AND GATE Truth Table to verify). Power or 1 at the base of the transistor keeps it from turning on (remember the arrow has to point toward the negative to work).

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Open

Sitting on the seat opens the seat belt switch and this reverses the voltage at the input of TR1 turning it on and triggering the buzzer.

Other Logic Symbols and their Truth Tables Truth Table for "OR" GATE

INPUTS

OUTPUT

 A

 

B

0

 

0

0

 

1

C  

 

0

1

1

 

0

 

1

1

 

1

 

1

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INTEGRATED INTEGRAT ED CIRCUITS

Truth Table for "NAND" GATE

INPUTS  A

 

OUTPUT

B

 

0

 

1

C

 

1

0 0

 

1 1

 

1

0

 

1

1

 

0

Truth Table for "NOR" GATE

INPUTS  A

 

OUTPUT

B

0

 

0

0

 

1

1

 

C

 

1

 

0

0

1

1

0  

0

Truth Table for "XOR" GATE

INPUTS

OUTPUT

 A

 

B

C

0

 

0

0

 

1

1

 

0

 

1

1

 

0

1

 

0

1

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CHAPTER 5

Truth Table for S-R Flip Flop

OUTPUT

INPUTS

S-R Flip Flip-Flop -Flop Symbol 

 A=S

 

B=R

0

 

1

 

0

1

 

0

 

1

0

 

0

1

 

1

C=Q

 

HOLD  

1

The S-R ip-op truth table has an added feature compared to previous tables. It can hold over a previous output when its two inputs are zero.

S-R FlipFlip-Flop Flop Symbol  in Detail 

HOLD MODE Used for  Memory 

Specically, a 0 input on A and a 0 input on B gives the Flip Flop the ability to hold over previous output values. This gives logic circuits the ability to have memory. Any input other than two zero' s will give the designated output shown in the truth table.

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CHAPTER 5

Chapter 5 Quiz

1)

How would you check the power to the operational amplier  as it is enclosed in the component box? 2)

Component pin 5 and 6 are two inputs which look  for a   in power between the two inputs to drive externall light circuit. externa

3)

In the AND Logic Gate below if the input on A is 0.2 volts and the input on B is 2.7 volts, what is the output voltage at C?

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4)

a. What is the output at point B if the switch is closed at point A?  b.   Will the above buzzer turn "on" based on the circuit above?

5)

The last S-R Flip Flop output at C was a 1. The previous unknown inputs are changed to 0 on A and 0 on B. What is the output at C?

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

Chapter 6 DIAGNOSTIC DIAGNOST IC PROCEDURE  PROCEDURE 

5 STEP SYSTEMATIC DIAGNOSIS Using a system approach to solve an electrical problem ensuress that you don' t miss the problem and nd it in the sure shortest amount of time. 1)  VERIFY THE COMPLAINT

Check that the symptom is as you understand it to be. Look  for related symptoms that may help in your diagnosis of the complaint. 2)  MAKE SOME QUICK CHECKS

Make a visual inspection of as much of the system that is assessable. You may have some extra inexpensive components lying around and could temporarily try switching them with the original component. Also make any quick tests of the circuit that you can. Check for any diagnostic codes if the system has a computer that can do this. 3)  RESEARCH AND ANALYZE THE SYSTEM

Determine what the system consists of and where it is using the EWD and any other information you have. Research as much of the system that you need to make an educated test of  the system. 4)  SPLIT THE CIRCUIT IN HALF

When testing an electrical circuit, test half way through the circuit. Then split the circuit in half again. By doing this you' ll nd the problem very quickly quickly without making many checks.

 

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DIAGNOSTIC DIAGNOST IC PROCEDURE

5) ISOLATE AND CORRECT THE PROBLEM Repair the problem correctly. Solder rather than crimp any connections that need repair.

FINDING FINDI NG A SHORT CIRCUIT Since a short circuit will blow a fuse rst. Replace the blown fuse with a digital voltmeter. Disconnect and reconnect the connectors while watching the voltmeter. The short lies between the connector where the voltmeter indicates source voltage and the connector where there is no voltage indication.

If you have a solid state component that failed check the output circuit it controls rst for a short. One quick way would be to disconnect connector A and check the resistance to ground using an ohmmeter. Reading a resistance of zero indicates a short. Disconnect the ground side of the circuit. If  the resistance is still zero keep disconnecting the circuit as you work your way back toward the meter. The point just before the meter starts reading higher resistance is where the short circuit is.

PRACTICAL AUTOMOTIVE ELECTRONI ELECTRONICS CS

 

CHAPTER 6

INTERMITTENT PROBLEMS These are the hardest of all problems to solve. Standard testing will not pinpoint the problem and usually is a waste of  ti me. Therefore learn as much as you can when the problem does occur. Try to determine if the problem occurs when the vehicle is rst started, on warm or rainy days, going over   bumps, etc. Then use similar circumstances circumstances to get the problem to reoccur. Sometimes you have to be inventive like using a heat gun to blow air on the component to simulate a hot day. Try getting the problem to reoccur by giggling wires, or driving over bumps to simulate the condition.

Check for loose pin connections at a component. One way to do this is to cut a pin from an old electrical harness and use it use  it as a test pin. Disconnect the connector from the harness and check, one by one, for a snug t of each connector.

Testing Connector with a Pin

Refrain from replacing parts, guessing, trying to x the system. Rather take a guess of the circuit you think is causing the problem based on the symptoms when it occurs. Then devise a test, in advance, to verify that you have found the  problem. Then operate the vehicle until the problem does reoccur. This way you' ll know for sure that you have veried and found the problem. Let the customer know in advance that you may have to keep his vehicle for several days with no guarantees guarantees of xing the problem if it doesn' doesn' t reoccur.

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74

DIAGNOSTIC DIAGNOSTI C PROCEDURE

02 SENSOR MONITOR CHECK Tapping in and monitoring the 02 sensor signal will verify whether the engine is operating close to stoichometric. This check will test the 02 sensor and many other components in the system. It' s best to use an analog voltmeter. voltmeter. This way you' ll have a needle that you can see uctuate uctuate between 0 and 1 volt (usually from 0.3 volts to 0.7 volts). The average should be 0.5 volts for a normal operating system. After the engine is warm check the 02 sensor. Create a vacuum leak big enough to drive the exhaust lean and cause a zero reading in the meter.

Then richen the mixture and cause the needle to go to one volt.

One can do this by substituting a different resistance in the water temperature sensor circuit fooling the computer to think the engine is cold. You may nd the meter will not swing both ways with this test, then replace the 02 sensor.  Now after verifying the sensor is good if the needle stays on 1 or 0 then you have something else in the system causing this lean or rich problem. You' ll have to look in other areas to solve this problem. Once you have found and repaired the  problem the 02 signal will uctuate indicating the system is  back to normal.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

CHAPTER 6

Chapter 6 Quiz

1)

The motor does not run and the 15 A fuse blows only when the switch is closed. What part of the circuit would you hook  the voltmeter in series; and how would you check for a short?

2)

 A 1987 Toyota Supra

A fuel injected vehicle will not pass an emissions test at idle. It is completely warm and uses a regular zirconia oxide sensor. After hooking up a voltmeter and tapping into the sensor  circuit it is found that the meter reads 0.3 volts and does not uctuate with the engine engine running at 2000 2000 RPM. An air leak  is introduced into the system. The system is reset to normal and an increase in the fuel mixture is introduced with no change to the sensor reading. What should the next step be?

75

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

76

ABBREVIATIONS AND GLOSSARY OF TERMS

EWD EW D

El Eleect ctri rica call Wiri Wiring ng Diag Diagra ram m Manu Manua al. Is an addi additi tion ona al aut automot omotiv ive e manu manual al lled with diagrams of the vehicles electrical system.

Combination Switch Combines Headlight Low and High Beams, Tail lights and Turn Signal Controll into one switch. Contro J/ J/B B

Ju Junc ncti tion on Bl Bloc ock, k, or bo box x wher wheree seve severa rall sp spli lice ce conn connec ecti tion onss are are lo loca cate ted. d.

A/T

 

Automatic Transmission  

M/T

Manual Transmission Transmission

 

 NO  NC

 

02

 

Normally Open Switch or Relay Normally Closed Switch or Relay Oxygen

E FI

Electronic Fuel Injection

THW

 

Water Temperature Sensor 

ECU

R 

Electronic Control Unit Computer    

Resistor 

E0,E1,E2

 

DVOM

Ground

Digital Volt Ohmeter  

VOM

 

Volt Ohmeter 

AC

 

Alternating Current

DC

 

Direct Current

Sec

 

Second Second of Time

RMS

 

Root Mean Square is a measurement measurement of AC voltage that typical AC meters read.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

77

V

 

Voltage is a unit of electrical pressure.

A

 

Amperage is a unit of electrical current. Ohms is a unit of electrical Resistance.

Amplitude

 

The size or amount of a particular quantity.

LED

 

Vcc

 

Constant voltage output, typically regulated.

KS

 

Airow Meter Output Signal

Vo

 

Voltage Output

VZ

Light Emitting Diode

 

Rated Zener Voltage  

EGO

Exhaust Gas Oxygen Sensor 

Forward Bias

 

Electrical Electrical component is hooked up with its positive lead toward the the  positive lead of the battery and its negative lead toward the negative lead of the battery.

Reverse Bias

 

Electrical Electrical component is hooked up with its positive positive lead toward the negative negat ive lead of the battery and its negative negative lead toward the positive lead of the battery.

0

0        

Infnity

 

Typically Typically a reading so high on a meter that it will not register. register.

TR1 TR2

Transistor Number 1

 

Transistor Number 2

Pola Polari rity ty

Conn Connec ecti tion onss in re rela lati tion on to th thee po posi siti tive ve and and ne nega gati tive ve si side dess of th the e batt batter ery y circuit.

Driver Driv er Transis Transistor tor

Main Output Output Transi Transisto storr whic which h carr carries ies most of the output output power. power.

PNP Transist Transistor or

Transis Transistor tor that that has two positi positive ve mat materi erials als separa separated ted by a negati negative ve material.

 NPN Transistor 

 

Transistor that has two negative materials separated by a positive material

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

78

S1

PIN MCU

 

Switch Number 1

 

Electrical connection to a component which is typically numbered.  

Microprocessor Control Unit (computer unit)

CHAPTER QUIZ QUESTION ANSWERS CHAPTER 1 connections ons but only 3 apply to this specic specic 1)   a. 9C and 3C 1) b. 3; 9C, 14C, 12C 1) c. 4 connecti headlight switch circuit. They are 11C, 13C, 20D.  2)  a. 5, 2) b. female, 2) c. connector A 3) a. pin 2, 3) b. pin 3 4)  pin 4 of connector A 5) a. close, 5) b. normally open CHAPTER 2 1)  Yes it increases  2)  10 ohms 3)  The voltage at the rheostat becomes less than battery voltage. 4)   battery, or source voltage 5)   4 volts 6)  0 volts, Remember voltage drops don' t occur until power ows through the circuit. 7) a. 10 volts, dim 7) b. 12 volts, since you are reading open circuit, or battery voltage. 8) a. 12 volts, 8) b. 6 amps. CHAPTER 3 1)  3 cycles per second, or 3 hertz 2) 2.82 volts peak to peak or p-p (peak=1.41 times RMS and then times 2 peaks). 3)  No, it does show the sensor is probably o. k., and the problem is probably elsewhere, but without checking the sensor with an oscilloscope you cannot verify the sensor is working perfectly. 4)  No, he should check the connectors and wiring to the sensor for continuity and if they are o.k. then replace the knock sensor. 5) No, since the 02 sensor is capable of producing a lean and rich voltage therefore the  problem is most likely a lean mixture in the system which could be caused by a vacuum leak  or a clogged fuel injector etc. CHAPTER 4 reverse bias direction (instead (instead of being innity). innity). 1)   Bad, It is shorted in the reverse 2)   Hook an analog ohmmeter (which uses more power than a digital meter) between terminals 1 and 2. Check the amount of resistance in this direction. direction. Reverse the meter' s leads and check  the amount of resistance in the reverse direction. If the ohms are equal in both direc- tions the diode is probably open (or shorted if 0 in both directions). Note: the resistance should be high in one direction and low in the opposite direction. 3)   High Voltage since the battery is using water. The alter alternator nator is not regulating regulating the voltage.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

79

4) No since it directs current away from the transistor. It also is not a direct short to ground. You could hook a voltmeter to point A and other lead to ground. Then trigger the switch. No voltage when the switch is closed indicates a possible short. CHAPTER 5 Typically EWD' s will not show the internal integrated integrated circuit circuit pins, 1)   Check input at pin 1. Typically therefore check all power going into the external unit. In this case we would check pin 2 also, to be on the safe side. 2)  difference 3)   0 volts since A' A' s input is equivalent equivalent to 0 volts. volts. 4)  a. Yes, typically the EWD does not show all the wire connections to the NOT Gate, including power. Looking at the truth table, 0 input results in a 1 output. 4) b. No, since 0 input on A sends a 1 output on B. Two 1 inputs on the AND Gate give a 1 output. Since we are applying power to an PNP transistor it will not turn on and drive the  buzzer. output put value. Had it been 0 then the 5)  1, since two zero' s always hold over the previous out output would also have been 0. CHAPTER 6 1)  Replace the 15A fuse with a digital voltmeter. Then open point F and apply the switch. If  there is no voltage reading then hook point F back up and open point K and apply the switch again. Work your way back opening parts of the circuit until you loose your voltage reading. The last spot prior to the voltage drop indicates where the short is. 2)  Replace the 02 sensor. It' s not reacting to changes in the sys system, tem, therefore it is bad.  Note: Newer O2 sensors require a scan tool to monitor their performance. performanc e.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

Chapter 7

83

Practical Applicatio Applications ns ........... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ................ ..... 83 Testing a Heater Relay ............ ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ....................83 .........83 Test it like testing an ECM ........... ...................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .................... ........ 83 How to check for a good ground ........... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .................... ........ 84 Battery Drain........... Drain ...................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ...............85 ...85 Initial Test Test to see if you have excessive battery drain........... drain ....................... ....................... ....................... ....................... ................... ........ 85 Battery Testing........ esting................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ...............88 ...88 Testing the Whole Starting System ............ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ......................89 ...........89 High Resistance in the Starting Circuit ........... ...................... ...................... ....................... ....................... ...................... ....................... ...................... .......... 90 High Amperage in the Starting Circuit ..................... ................................ ....................... ....................... ....................... ....................... ...................... ............. 90 Charging Systems........... Systems ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .................91 .....91 Computer Systems need Constant Direct Current.............. Current.......................... ....................... ...................... ....................... ....................... ..................92 .......92 Testing for AC Ripple ........... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ................ ..... 92 Battery Sensor................................ Sensor............................................ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .............93 ..93 Modern Narrow Band O2 Sensors ............ ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .............94 .94 Wide Band O2 Sensors Sensors.......... ..................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... .............. ... 95 A/F Sensor Heater Circuit............................... Circuit........................................... ....................... ...................... ....................... ....................... ...................... ....................... ...................96 .......96 Single Computer Module Circuit Diagnostics ............ ....................... ...................... ....................... ....................... ...................... ....................... .................97 .....97 To Test Both Sensors and Cat with Scan Tool...... ool................. ....................... ....................... ...................... ....................... ....................... ......................98 ...........98 A/F Sensor Reference Voltages ........... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ...................... .......... 99 Active A/F Control Test by ECU ........... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ...................... .......... 99 Open Loop................ Loop........................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ................ ..... 100 Closed Loop........... Loop...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .................. ....... 100 AF/O2 Sensor Running Lean.............. Lean.......................... ....................... ...................... ....................... ....................... ...................... ....................... ...................... .......... 101 AF/O2 rich on both banks............... banks........................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... .............. ... 101 Hot Wire Mass Air Flow (MAF) Sensor .......... ...................... ....................... ...................... ....................... ....................... ....................... ....................... ................102 .....102 Fuel Tr Trim im Diagnostics........... Diagnostics ...................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ....................103 .........103 V6 & V8 Engines ....................... .................................. ...................... ....................... ....................... ....................... ....................... ...................... ....................... ...................... .......... 104 Leaking or Stuck closed Fuel Injector Test........ Test.................... ....................... ....................... ....................... ...................... ....................... ................ .... 105 Volumetric Efciency (V (V.E.) .E.) Test .......... ...................... ....................... ...................... ....................... ....................... ...................... ....................... .................... ........ 105 Use V.E. V.E. And O2 for further diagnostics ........... ...................... ...................... ....................... ....................... ...................... ....................... .................. ...... 106 Autel MK/MS 906 BT Automotive Automotive Scan Tool ........... ...................... ....................... ....................... ...................... ....................... ....................... ..................107 .......107 Fuel Tr Trims ims and Misre Monitor Diagnosis .......... ..................... ....................... ....................... ....................... ....................... ...................... ......................108 ...........108

 

Using PIDS Alone to Test.................. est.............................. ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .....................109 .........109 Bidirectional Bidirectio nal Testing Advantage.................. Advantage............................. ....................... ....................... ...................... ....................... ....................... ...................... ....................... .....................109 .........109 Doing a Bidirectional Bidirectional Test ..................... ................................. ....................... ...................... ....................... ....................... ....................... ....................... ...................... .................... ......... 110 Automotive Automot ive Oscilloscope ........... ...................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ............... .... 111 111 Toyota 4 wire COP combines ignition coil and igniter..................... igniter................................ ....................... ....................... ...................... ....................... .................113 .....113 Using a Low Current Amp Clamp .......... ..................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ...............115 ....115 Current Ramping Ignition Coils ....................... .................................. ...................... ....................... ....................... ...................... ....................... ....................... ...................... .................116 ......116 Fuel Pump Current Draw Test .......... ...................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .....................119 .........119 Toyota Standard EFI Fuel Pump System........... System...................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ...............120 ....120 Testing for an Open Fuel Injector Circuit........... Circuit ...................... ...................... ....................... ....................... ....................... ....................... ...................... .................. ....... 121 GDI Fuel System with PWM Fuel Pump.... Pump................ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ................ ..... 122 Gas Direct Injection (GDI)..................... (GDI)................................. ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .................122 ......122 Controlling Control ling Power ON .......... ..................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .......................123 ...........123 Power Side Switching Switching........... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ............... ... 123 Ground Side Switching............... Switching.......................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... .................... ......... 123 Relative Compression Test............ est....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .............124 ..124 Use Relative Compression Test to check for correct valve timing...............................................................126 Cam Crank Correlation Method of checking Timing ............ ....................... ...................... ....................... ....................... ...................... ....................... .................127 .....127 Variable Var iable Val Valve ve Timing (VVT (VVT-i) -i) .......... ...................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .....................128 .........128 Electronic Throttle Control............................. Control........................................ ...................... ....................... ....................... ...................... ....................... ....................... ....................... ...................130 .......130 Smart Stop Technology and Electronic Throttle Integration.............. Integration......................... ....................... ....................... ...................... .................. ....... 132 Using Scan Tools Record Feature .......... ...................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .................. ....... 132 Example: Using the Record Feature on the 906 BT Scan Tool Tool ..................... ................................. ....................... ...................... .................. ....... 133 Toyota Key off Evap System ........... ...................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... .......................134 ...........134 Troubleshooting roubleshooting the Evap System................... System.............................. ...................... ....................... ....................... ...................... ....................... ....................... ...................... .................137 ......137 Modern cars use Multiplexing Multiplexing .......... ...................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... .....................138 .........138 Basic Can System .......... ...................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... .................139 ......139 Can Main Bus Line ........... ...................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... .................... ......... 139 Sub Bus ........... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... .............. 140 Can Bus Network with Junction Connecto Connectors........... rs....................... ....................... ...................... ....................... ....................... ....................... ...................... .......... 141  Y  You ou need a Bi-Directional Bi-Directional Scan Tool .......... ...................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... .............. ... 142 Digital Multimeter use with CAN ....................... .................................. ....................... ....................... ...................... ....................... ....................... ...................... .................... ......... 142 U Codes Codes.......... ...................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... .......................143 ...........143 History Codes ....................... .................................. ....................... ....................... ...................... ....................... ....................... ....................... ....................... ...................... ....................... .......................143 ...........143

Take advantage of what the scan tool can do ....................... .................................. ...................... ....................... ....................... ...................... .................... ......... 143

 

Using a Breakout Box .......... ..................... ....................... ....................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ............144 144 Bus Fully Awake at 2.5 Volts ........... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ..................145 ......145 Bus Voltage using a DMM Meter ............ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ............145 .145 Scanning shows one module does not communicate......... communicate..................... ....................... ....................... ....................... ...................... ................... ........ 146 Alternate Voltage Method: .......... ...................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ............146 .146 Scanning shows two or more modules do not communicate......... communicate.................... ....................... ....................... ...................... ................... ........ 147 Split Half Search........... Search ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ................147 .....147 Normal H. S. Can Waveforms Waveforms ............ ....................... ...................... ....................... ....................... ...................... ....................... ....................... ...................... ....................... ............148 148 Use the scope to check for an intermittent signals ...................... .................................. ....................... ...................... ....................... ................149 ....149 Using an oscilloscope to check the Can waveform..................... waveform................................. ....................... ...................... ....................... ....................... ...........149 149 Open Terminating Resistor................... Resistor............................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ................... ........ 149 Checking the 5 volt reference circuit ....................... ................................... ....................... ...................... ....................... ....................... ...................... ..................... .......... 150 Can Signal Direction .......... ...................... ....................... ...................... ....................... ....................... ...................... ....................... ....................... ....................... ....................... ............... .... 151 Take Care when Replacing Computer Modules..... Modules................. ....................... ...................... ....................... ....................... ....................... ....................... ...........152 152

 

83

Chapter 7 Practical Prac tical Applica Application tions s Relay Rela y Box

Testing a Heater Relay 5

Relay Rela y Socket Socket

4

1

3

Blower Blow er Swit Switch ch

To test a relay rst nd its location, and wiring diagram for  it, in the service repair manual.

Test it like testing an ECM When plugged in it is very difcult to access the relay’s connections. Therefore unplug it and test all the wiring inputs and outputs connected to it. Condemn the relay if all the wiring tests ok (assuming no connection problem).

Pin 5

Pin 2

Hot all the time

Hot with key turned on

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

84 How to check for a good ground To check for a ground rst hook the test light lead to a  positive terminal of the power source. Now when the light touches a good ground (instead of power) it lights up.

Pin 4

Use a powe Use power/ r/gr grou ound nd fuse fused d ad adap apte terr in the the vehicl vehicle’ e’s s cig cigar aret ette te light lighter er socke sockett

Pin 1

Li Lig ghts hts wh when en swit switch ch is tu turn rned ed from from of offf to lo low w sh show owin ing g a go good od gr grou ound nd

Good Goo d gro ground und

Pin 3

Fu Fuse sed d po pow wer is ju jump mped ed to fan fan mo moto torr caus causin ing g fan fan to turn turn on lo low w spee speed d

Final test - after the rest of the circuit tests ok, if fan does not come on with relay plugged in then replace the relay.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

85 Battery Drain More recently recently known as Parasitic Drain, it can cause your   battery to die overnight, or even sooner if the amp draw is high enough. When modern vehicle computer systems fail to go to sleep, after the vehicle is turned turned off, an excessive excessive amperage can drain the battery.

 mp Clamp that has a 2 mp Range

Still, some current is required to keep the computer  Still, memory alive, and the standard is approximately .035 to .050 Amps (or 35 to 50 mA) on modern vehicles. Anything more can cause a problem, depending on the amount of  amp draw and how big the vehicle’s battery is. To test for drain I’ve found using a low amp clamp that can measure a 2 amp range is best. As it takes 30 minutes to an hour, or so, for the system to go to sleep before you can take your measurement. Assuming the vehicle has been sitting sitt ing for some time, if you disconnect disconnect the battery to hook  up a standard (in-line) amp meter, you will have to wait an addition hour to take your reading. This is also true if you  pull a fuse (more on this later).

Initial Test to see if you have excessive battery drain

Rend Re nder er door door swit switch ch clos closed ed

• Step Step 1 make make sure sure the the batte battery ry is fully fully charg charged. ed. Make Make sure vehicle doors are closed and key fobs removed from the vehicle area. If you need to keep the doors open, then render the locks in a closed position by some mechanical mechanical means. Remove any bulbs used for the hood light.

Prior to clamping the meter on the wire hold it perpendicular and close.Then hit the zero button. Clamp has to fully close when taking measurement.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

86 After 30 minutes, to an hour or so, take your low amp clamp and zero the meter. Then clamp it around your  negative battery cable and take a reading. If 50 mA or less then you are done. You do not have a drain. If more than 50 mA go to step 2. • Step 2 to isolate isolate which which fuse circuit(s) circuit(s) is causing causing the the drain, use a digital digital voltmeter to test the voltage voltage drop across across each fuse (one by one).The fuse with the most voltage drop is your problem circuit.

17 m is wi withi thin n sp spec eci ica catio tions ns

Use a conversion chart, based on the type and size of the fuse, in order to nd the current draw (amount of  amperage) ampera ge) it is putting out. These charts charts can be easily obtained by researching them on the internet.

Chec Ch eck k volt voltag age e dr drop op acro across ss each each fuse fuse

I turned vehicle’s interior dome light on to get 4.6 mV drop across 10 amp mini fuse which equals a 620 mA drain on the battery.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

87 An alternative is to pull fuses (one at a time) and watch for  the amp clamp amperage to reduce to zero, or close to it. The potential problem here is if you put a fuse back in (that had no amp draw) it just might wake up the computer  module and cause normal momentary momentary high amp ow which would confuse your test results! • Step Step 3 use the the facto factory ry wirin wiring g diagra diagram m to help help isola isolate te the the  problem by disconnecting the circuit at different areas until the amp drain goes away. The last place just before your  disconnection is most likely the problem.  Note: I say most likely because a vehicle with multiple computer comput er modules can have a different different circuit wake up your current test circuit. If your current test circuit is part of  the network bus, you may have to isolate it from the rest of  the bus and retest before the item/part in question can be considered bad. • Step Step 4 after after the repai repairr retest retest to verif verify y the job job is complete.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

88

Battery Testing

12.80 V

12.66

12.70 V 12.66 V

100%

12.58 V

90%

12.51 V

80%

12.45 V

70%

12.35 V

60%

12.28 V

50%

12.20 V

40%

12.12 V

30%

12.02 V 11.97 V

20% 10%

11.89 V

0%

• Test Test 1 any time time the car car sits sits for any llengt ength h of time time check  check  its open circuit voltage (O.C.V.). If below 12.58 volts trickle trick le charge for 4 hours. Checking O.C.V. If at rst you read 10.55 volts you have a shorted cell and won’t be able to jump start the vehicle.

Rule: Always check O.C.V. before testing the system or jump starting the vehicle.

Alternately if you only have 0.5 volts you have an open cell and the vehicle can be jump started but the vehicle is running off the alternator and can cause increased voltage which could damage other electrical circuits. Lastly, if your O.C.V. Is over 13 volts it is likely low on water. Checking the water level, if a plate is showing dry don’t add water as chances are the battery is on its way out.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

89 Testing the Whole Starting System

Starti Sta rting ng Volt oltage age

• Test Test 2 Hook Hook a Digita Digitall Multi Multimet meter er (DMM (DMM)) to the  positive and an d negative terminals of the battery. Push P ush the  button to adjust the Min/Max setting in the meter. Start the engine 3 to 6 times. Minimum Minim um voltage should not drop below 10.0 volts. volts. • Test Test 3 Batter Battery y Rechar Recharge ge Curre Current nt Te Test. st. Hook Hook a low low amp amp clamp around the negative battery terminal and start the vehicle. The amp ow back into the battery should be less than 10 amps after 5 minutes of recharging, once the engine is started. start ed. Anything more than 10 amps can cause serious damage to the alternator’ alternator’ss diodes and the battery should be replaced.

17.3 mV at 10 mV per mp Gi Give ves s 1.73 1.73 mp mps s Rech Re char arge ge Ra Rate te OK

• Test Test 4 Use a good good batter battery y tester tester to to verify verify the the batter battery y is good. If Tests 2, 3 and 4 all pass then the whole starting system is good. Now move on to testing the charging system.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

90 High Resistance Resistance in the Starti Starting ng Circuit Allow a voltage drop of 0.5Volts per cable.

If the vehicle does not crank and battery voltage does not drop when engaging the starting system, you most likely have a high resistance in the starting circuit. What technicians have been taught for years is to have one  person tap on the starter with a wrench while the other  engages the starting system. If the vehicle now starts (when it would not prior to tapping on the it) then the problem is with the starter itself. If you are without a digital meter have someone turn the headlights on and then try and start the car. If the lights don’t dim it is also an indication of an open, or high resistance in the starter circuit.

Test each cable separately while cranking the engine.

A way to get at the heart of the problem is to start your  tests at the starter relay (not shown). To test the starter  relay refer to my section on testing a heater relay. After  testing test ing the relay and switch circuit, the next step would be to do a voltage drop test on the starter cables. If the cables test good and battery is ok then replace the starter motor  and solenoid.

High Amperag Amperage e in the Starting Circu Circuit it If the battery voltage drops below 10.0 Volts during cranking you can suspect there might be high amperage in the starter circuit but you cannot rule out the possibility of  having a bad battery. Therefore use a battery tester to test the cold cranking amps (CCA) and compare them to what the battery is rated for. A seized engine could draw high amperage as well. In crank position, if the engine did not turn over even once you may need to check for free rotation by putting a wrench on the crank bolt to see if it will rotate by hand? If  it is ok then your high amperage problem is most likely a  bad starter.

Rule:

After 4 and ½ years this cars 60 month  battery rated at 540 CCA tests at 373 CCA. It

Verify battery is good using a battery tester   before condemning the starter.

still starts the vehicle but needs to be replaced. Cranking voltage below 10 volts.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

91 Charging Systems Generator Load Test 20

.5

10

 Amp Clamp  AMPS

B

S

IG

IC Regulator Regulator

With engine running, load alternator by turning headlamps on hi, fan on high, and other electrical accessories. Should be able to see 30 amps output minimum.

L

ECM

Troubleshooting involves checking all the wire inputs to the alternator before condemning it. M terminal to the ECM will be a pulse width modulated modulated signal.

 lternator

Com o Meter

The alternator powers the electrical system and recharges the battery while the engine is running. Typical charging voltages measured across the battery are 13.8 to 14.2 Volts. Yet on newer vehicles where the computer controls the alternator voltages, they can be as low as 12.6 volts and as high as 15 volts. To test some Hyundais you may see 12.8 volts at idle. So check voltage with a load, such as turning on the headlights, and increasing the RPM (which will increase voltage) before deciding to replace the alternator.  Note: On Ford Smart Charging Systems you can disconnect the 3  pin connector at the alternator, it should cause it to put out 13.8 volts showing that the alternator is good.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

92

Computer System Computer Systems s need Constant Direct Current The alternator uses several diodes to change AC to DC voltage and current which the vehicle can use. When one or  more diodes fail, AC can creep into the electrical system and create problems with the CAN bus. The overall amperage output also decreases.

Testing fo forr AC Ripple

Normal Ripple

The test can only be done on a fully charged battery. • Hook an oscillo oscilloscope scope to the the positi positive ve and and negative negative leads of the battery. battery. • Set tthe he volta voltage ge to AC AC volts volts whic which h blocks blocks the the 12 volt volt DC signal. Set the scale to less than 1 volt. • Adjust Adjust the the time time settin setting g to match the normal normal ripple ripple  pattern shown in this section.

Open Diode

• Sta Start rt the the car car and load load the alte alterna rnator tor by by turnin turning g on the the headlights, heater fan motor and other accessories. Raise the RPM to above 1800 and read the ripple voltage. Peak ripple voltage should not be over 100 mV. More importantly is to view the pattern on the oscilloscope. If the  pattern is not normal, the alternator is most likely bad. See sample patterns. Caution:

Open Stator 

Vehicles like Hyundais may not show any AC Ripple at idle as the charging charging system operates so little then. Any CAN problems may not show up until you increase engine speed.  Note: Refer to “Automotive Oscilloscope” and “Current Amp Clamp” explained later in this publication.

Shorted Stator 

 

93 Battery Sensor 

Dodge Power Po wer Distri Distri ution ution Center

Body Control Module

Inte In tellllig igen entt Batt Batter ery y Sens Sensor or

12 V Car Battery

+12 V

+

Electron Elec tronic ic Batt Battery ery Sensor Sensor

The battery sensor is connected to the negative battery terminal. It measures current, voltage and temperature of  the battery. It helps maximize battery life by avoiding deep discharge and improves fuel economy. Symptoms caused by sensor not working properly:

Li Lin n Bus Bus

•

Engi Engine ne Surg Surgin ing g

•

Low Low Batte Battery ry Volt Voltag agee

•

Ill Illumi uminat nated ed Batt Battery ery Light Light will will be be on on

Codes for it will show up on the scan tool. Example: U113E-00 Lost Communication with Intelligent Battery Sensor  (BCM)

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

94 Modern Narrow Band O2 Sensors

O2 Sensor 

O2 Sensor 

From Engine

Graph on Scan Tool

CAT

0.5 Volts

0.5 Volts

Modern vehicles have an additional O2 Sensor at the rear  of the Catalytic Converter (CAT) to monitor its efciency. To improve operation, operation, O2 Sensors Sensors now employ a heater  circuit to get the sensor up to operating temperature range quickly.

ECM

+B OX

O2 Sensor  HT

Heater Element

The heater element is energized with approximately 2 amps until the engine is warmed up and then the ECM turns it off.  Note: No need to test the heater circuit if a heater code is not indicated on the scan tool.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

95 Wide Band O2 Sensors

 A/F Sensor 

O2 Sensor 

CAT

Note: A/F Sensors should not oscillate like a front O2 sensor. If you see this on the scan tool check to see if the  A/F Sensor was accidentally replaced with a less expensive O2 Sensor. They are not interchangeable. Purchase the dealer brand using the vehicles vehic les serial number to look up the correct part.

Air Fuel Sensors work faster over a wider range to improve emissions and typically are used in front of the CAT with a traditional O2 sensor installed behind. The A/F Sensor  does not create its own voltage but works off current. Their  operation can only be viewed using a scan tool.

 A/F Sensor 

1. To test wire integrity verify voltage from ECU using a DVOM

 AF+

 AF-

ECU

2.9 V 2.9V

2. Next check other side for approx. 3.3 V

3.  An LED computer safe test light can be used in a similar manner to see a reaction on scan tool to test the ECU.

 

Current Flow Detector 

3.3V

A 0.4 volt EMF differential is continuously applied across terminals AF+ and AF- to balance out zero current ow creating a stoichiometric condition. A lean condition causes less than 0.4 Volts and is higher at AF+ causing positive causing  positive current to ow from ow  from AF+ to AF-. Reference voltage on the scan tool will increase Reference increase over 3.3V. ECU then increases the fuel injector duration to compensate and maintain the perfect air/fuel ratio.

 Note: A rich condition c ondition creates just the opposite effect. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

96

A/F Sensor Heater Circui Circuitt

ECM

 A/F Relay

MREL  A/F+

 A/F Sensor 

 A/F-

Heater Element Duty Cycle

Note: If get an exhaust sensor code of “Heater  Circuit High” that is typically an indication of  a bad ground. Check the

A/F sensor operates at 1200 F and must heat up fast. An A/F relay is required as it carries up to 9.9 amps to produce additional heat. The heater circuit is pulse width

ECM ground.

modulated. When cold the duty ratio is high. It can be monitored on a scan tool. If circuit fails it will set a code and will turn off the circuit. The scan tool will indicate an open loop condition. The heater element of the sensor can be measured using an ohmmeter.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

97

Single Computer Module Circuit Diagnostics

ECM

 A/F Relay

MREL  A/F+

 A/F Sensor 

 A/F-

+ Duty Cycle

Simplied Example

Scope

Basic diagnostic steps on a single computer module are to test the inputs to the ECM and then the outputs (including all powers and grounds). If all are good then condemn the computer. Inputs: MREL - check for 12 V power at the ECM

Note: Replacing the computer module will typically require some reprogramming before it will function.

ECM ground - check for a good ground Output: A/F+ Check for voltage voltage A/F- Check for voltage AF Relay heater power to ECM - Check for duty cycle  power going into the ECM. Outputs can be checked using the scan tool data info and/or veried veried with a voltmeter or scope.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

98 Drive steady for some time  before viewing rear o2 sensor data

 A/F Sensor 

Stoichiometric

O2 Sensor 

From Engine

Toyota B1S1 B1S 1 3.3 Volt Volts s

CAT

0.5 Volts

B1S1   0 mA Current

Higher than 3.3 V indicates a lean condition with A/F sensor.

Compared To

Higher than 0.5 V indicates a rich condition with O2 sensor.

To Test Both Sensors and Cat with Scan Tool 1) Warm engin enginee until rear O2 Sensor Sensor stays steady steady 2) Rev engin enginee and let off accelerator. accelerator. 3) The front sens sensor or should uctuate uctuate a lot where the rear  sensor will only move a little.  Note: If either sensor stays steady introduce propane to richen the mixture. Then add a vacuum leak to lean the mixture. mixtu re. One sensor does not react? It is most likely bad. Test computer and wiring before condemning the sensor. Also check to make sure there are not any exhaust leaks around sensor that may skew the scan tool readings readings too.

Front A/F Sensor 

Rear O2 Sensor 

If rear O2 sensor sensor swings wide like front A/F sensor (same amplitude), it is possible the CAT is bad. View Mode 6 data to verify if the CAT number is getting close to failing

the test by comparing comparing it to outer limits indicating indicating it may fail in the near future. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

99 Active A/F Cont Control rol T Test est by ECU

1.026

 A/F Ratio

0.956

 A/F Sensor 

3.3 Volts

Normal Self Test during driving

During driving, the ECM tests for malfunctions in the A/F Sensor, O2 Sensor(s) and the three-way catalytic converter. It force drives the fuel injecto injectors rs rich and lean. Don’t confuse this with an air fuel variance problem. If a real  problem exists the ECM will set a code.

A/F Sensor Reference Voltages Toyota uses 3.3 for stoichiometric. and GM use 2.6 volts as avolts reference guide on theirBosch scan tool. Different manufacturers use different reference voltages. Honda A/F sensors react just the opposite of Toyota!

RULE: WHEN IN DOUBT USE LAMBDA Use Lambda instead of watching watching voltage or current current ow on the scan tool to verify if the A/F Sensor is working  properly. Lambda is the actual air fuel ratio calculated by the ECM  based on the air fuel ratio sensor output. A lambda value of  1.000 equals the stoichiometric stoichiometric ratio of 14.7 to 1. Most genericc scan tools have a lambda (PID) reading. generi reading.

Scan Tool A/F Sensor Lean Condition (Toyota) AF Lambda B1S1 1.147 1.147 AFS Voltage B1S1 3.88 V AFS Current B1S1 0.36 mA (positive current) For example: a Lambda of 0.872 on B1S1 would indicate a

rich condition.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

100 Closed Loop Short Term F.T. Eventually Learned Long Term F.T.

• Warm Engine Engine • Idle

ECM

• Cr Crui uise se

Calculates O2/A/F reports

 

ECM cycles fuel:

Fuel Trim

to +10% Fuel to -10% Fuel

Injectors

O2/A/F sensor 

Combustion

When the ECM ignores exhaust sensor sensor information information it is known as “open loop.”

Open Loop

• Cold Cold Eng Engine ine • Accele Accelerat ration ion

ECM

Last Long Term percentage remains in OL unless memory is cleared by disconnecting battery

Long Term Fuel Trim

Injectors

Combustion

On some vehicles, vehicles, to temporaril temporarily y clear Long Term Fuel Trim Memory from open loop disconnect disconnect the  battery for 60 seconds.

 Note: Short and Long Term Fuel Trims are additive but when one is a positive number and the other is a

negative number you subtract one from the other. Fuel Trims over 10 % indicate a problem with the engine. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

101 AF/O2 Sensor Running Lean •

Do Injecto Injectorr Volume Volume Active Active Test with the scan scan tool tool to to set car in open loop (OL). First store any codes and check freeze frame data. Disconnect negative battery cable to clear long term fuel trim.

Leave at 0%. Engine runs better suspect faulty exhaust sensor. Drive 25% rich. If engine runs better check for wrong fuel, low fuel pressure, restricted injectors etc.  Note: An alternative method would be to add propane in the intake after disconnecting the negative battery cable. But system would be in closed loop so results may be skewed somewhat.

 AF/O2 Sensor lean on one bank Rule:

•

Do IInje njecto ctorr Volume Volume Acti Active ve Test Test at at + 25%. 25%.

Do a Relative Compression Test rst, any time you have a bank specic issue. As cam timing issues can affect fuel trims and resemble resem ble vacuum leaks sending you in the wrong direction.

Lean AF/O2 sensor responds. No? Replace sensor (after  checking wiring). Ok. Then check for an exhaust or vacuum leak on bank  where AF/O2 sensor responded. Also inspect for restricted or inoperable injector(s).

AF/O2 rich on both banks •

Cle Clean an MAF Sensor Sensor or or swap swap with with a known known good part. part. Fuel trims returned to normal. Ok.

•

Pin Pinch ch off off the the PCV v valv alve. e. Now Now ok. Gas in in oil. oil.

•

Blo Block ck Purge Purge line. line. Now Now ok. Stuc Stuck k open purg purgee valve. valve.

•

Che Check ck for hig high h fuel fuel pressu pressure. re.

•

Check for a st stuck uck open open inject injector. or. Turn individual individual injectors off, using scan tool, one at a time, and see that AF/O2 voltage voltage drops to near zero.

 Note: Rear O2 sensor should follow the front sensor. If  front sensor goes rich then the rear O2 sensor should go

rich too. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

102 Hot Wire Mass Air Flow (MAF) Sensor 

    c     e     s       /     g     w     o       l       F     r       i       A

Platinum Hotwire

 

200 150 100 50 0

1.8v

2.8v

3.6v

4.4v

Voltage

(Heater) Thermistor  Intake Air Flow Note: A quick test of the MAF Sensor  problem is to disconnect it to see if the vehicle starts or run better? As ECM will default to a known good value.

The MAF Sensor converts the volume of air drawn into the engine into a voltage signal. The thermistor resistance changes with temperature and the voltage across it will then vary. As more air passes the hot wire it cools down. The ECM sends more current through the hot wire to maintain temperature. The ECM outputs a voltage signal in  proportion to the hot wire current allowing the ECM to determine engine load. •

Bas Basic ic MAF MAF Key On On Engine Engine Off Off (K (KOEO OEO)) Test. Test. Check  Check  30 seconds after key is turned on. The scan tool live data should show 0.49 grams per second or less. A higher number here may indicate a contaminated sensor hot wire and require cleaning?

 Note: Some S ome GM MAF S Sensors ensors generate gene rate a square wave wa ve frequency similar to Toyota’s Karman Vortex Air Flow Meter. Using a Graphing Multimeter set to frequency is helpful in diagnosing glitches in its circuit.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

   

103

Input

 

Computer  Process

Output

Mass Air Flow Sensor 

E C M

Crank Position Sensor 

Injectors Data Link Connector 

O2 or A/F Sensor  Example: ECM takes inputs from sensors, processes the information, and then outputs the correct amount of fuel to the engine via the fuel injectors.

With ever increasing computer systems, use and diagnostics with scan tool equipment is essential in Practical Automotive Electronics. After a repair involving a computer computer component, an initialization may be required using the scan tool, else the vehicle may not run properly. Most high end scan tools have this feature. On some vehicles disconnecting the vehicle’s battery is all that is needed.

Fuel Trim Diagnostics •

If you you have have a misr misring ing engine engine look to your your fuel fuel tr trims ims on the scan tool. A single single cylinder cylinder misre from spark  will hardly increase fuel trim. Yet a misre caused by a fuel problem will greatly change fuel trim numbers either positive or negative.

•

If tthe he engine engine is is misri misring ng bad enoug enough h to kick kick it into into open loop (OL) the fuel trim numbers are useless. Catch the problem in closed loop (CL) on the scan tool for proper diagnosis.

•

Look for a proble problem m when when fuel fuel trim trim numbers numbers climb over  10%.

Don t overlook overlook fuel fuel content for contam contaminati ination. on.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

104 +15%

Fuel Trim

•

0% 3500 RPM

Idle

A Fuel Trim over 10% 10% positive positive at idle idle that decreases decreases at higher RPM speeds indicates indicates a vacuum leak. Block off  the brake booster. Check for vacuum on the dipstick  dipstick  tube indicating an internal vacuum leak. Smoke test the intake to nd the leak.

Fuel Trim

Idle

•

A Fue Fuell Trim Trim over 10% that that goes goes from from negat negative ive to to more more  positive at higher RPM speeds spee ds indicates a dirty or bad MAF sensor. Try cleaning the MAF sensor.

•

A Fue Fuell Trim Trim over over 10 % (high (high or low) low) that that do does es not not change with engine RPM indicates a biased A/F or O2 sensor. senso r. Verify by adding propane into the intak intakee or 

+15%

3500 RPM

-15%

apply a vacuum leak. The sensor(s) reading should change if it is good.

V6 & V8 Engines

Fuel Trim

•

+20%

A Fue Fuell Trim Trim that that goes goes negat negative ive on on one bank bank and and  positive on the other bank could have a bad AF/O2 sensor, leaking injector, bad CAT or worn timing chain (will be on the side with the negative Fuel Trim number).

Idle

 

3500 RPM

•

A Fue Fuell Trim Trim that that is over over 10% 10% negativ negativee at idle idle and above:

Pinch off the PCV valve to see if fuel in the oil. Block off the Purge Valve to see if valve is stuck open. Shut off an injector, one at a time, and O2 voltage should drop to zero.

Fuel Trim

Idle -25%

3500 RPM

Introduce a vacuum leak to see if it runs better. Then check  for a fuel injector leak.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

105

Leaking or Stuck closed Fuel Injector Test •

Use scan scan tool’s tool’s bidirection bidirectional al test test to shut shut the the problem problem injector off and watch the O2/AF sensor go lean.

If O2/AF is rich and stays rich it most likely is stuck open. Verify by doing a fuel rail leak down pressure test. If O2/AF was lean to begin with and has no change when injector is turned off it is most likely stuck closed assuming electrical side of circuit tests ok?

Volumetric Efciency (V (V.E.) .E.) Test This test veries good engine breathing and that you have a good functioning MAF sensor. Rule of Thumb: •

Run vehicle vehicle at wide wide open open throttl throttlee in rst gear and measure measu re the MAF’s grams per second (g/s) at 5000 RPM. For a standard overhead valve engine use 40 x engine size size in liters. Example: Example: 4.0 L times 40 equals 160 g/s.

For a dual overhead VVT engine use 50 times the engine size in Liters. If minimum number in grams per second is not met you have a breathing breathing problem (such as a restricted restricted exhaust) or a  bad MAF sensor (on MAF equipped e quipped engines). An alternative alternative is to use the “Calculated “Calculated Load” number on the scan tool. It should be over 90%.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

106

Use V.E. V.E. And O2 for further diagno diagnostics stics •

Gra Graph ph both both V.E. V.E. and O2/AF O2/AF at at wide wide open thro throttl ttle. e. If  O2/AF is low and V.E. is high - have a fuel starvation  problem. Check Ch eck fuel pressure and fuel injectors.

If O2/AF is low and V.E. is low - have a problem with MAF sensor. If O2/AF is high and V.E. is low - have a restricted intake or exhaust. Graph the MAF voltage. If it looks glitchy and have a code for the CAT then replace it. On a speed density engine that uses a MAP sensor: •

Use a v vacuu acuum m gauge gauge to diagn diagnose ose probl problems ems.. Or on the the scan tool you can read vacuum by taking the baro reading and subtract the MAP reading to give you engine vacuum.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

107 Autel MK/MS 906 BT Automotive Scan Tool

This is a profession professional al auto shop level scan tool which uses a remote bluetooth (BT) dongel allowing one to view the tablet freely from inside (as well as outside) the vehicle. The MS and MK 906 BT (mine) are both exactly the same except the MK version has multiple languages where the MS is only in English.

Dealer Side of MK 906 BT

Most manufacturer (mfg) repair manuals require you to use their specic dealer scan tool. You can use the 906 BT in  place of the dealer version. It does do es everything e verything except  programming. You Yo u still need to go to the dealership for  that! A thirty dollar code reader will let you read generic codes in the ECM only. The 906 BT reads generic and manufacturer codes in all the vehicle’s modules plus has  bidirectional ability. Lets jump into what I consider important for you to know when using the 906 BT to diagnose misres. Two Sides to this Scan Tool

There is the generic side and then there is the dealer side of  this tool. To get the extra dealer information you have to  back out of the generic side and open the dealer side. Both Bo th sides have important information. So get use to opening and viewing both of them. The manufactur manufacturer er has extra codes that the generic side does not have. But what do you do when you have an intermittent misre yet don’t see any codes when using the scan tool? You need to access the generic side of the scan tool and look up the  misfre monitors.

Note: Generic side has Fuel Trims too but less other info.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

108 Fuel Trims and Misre Monitor Monitor Diagn Diagnosis osis Access the generic side of the scan tool and go to Mode 6: •

Check out EWMA EWMA misre misre counts counts for for previous previous driving driving cycles. EWMA stands for Exponentially Weighted Moving Average and saves up any previous drive cycle misres per cylinder.

•

Loo Look k at all all cylind cylinders ers and and the one one with with the the bigges biggestt misre number is your problem cylinder. Note that sometimes an adjacent cylinder in the ring order will appear to have misres. This is normal as the ECM monitors the crank sensor signal for variations in  power pulses and this sometimes happens.

•

Now y you ou can run run other other test testss to deter determin minee why that that specic cylinder is misring.

Generic side of MK 906 BT

Assuming that the fuel trim info is normal (else look at the injectors etc).

Cylinder number one is not a problem cylinder but if it were the number would be much much higher!

•

Swap the the problem problem cylinde cylinder’s r’s coil coil ((if if COP COP coil coil)) with with a known good cylinder and drive the vehicle. If problem misre moves to another cylinder then the swapped coil is faulty.

•

Els Elsee swap swap the spar spark k plug to to a known known good cyli cylinde nder. r.  Now if problem moves mov es to a different cylinder, viewing the scan tool, you know the moved spark plug was the  problem.

If misre did not move make sure the electrical electrical circuit to that specic coil is functioning before looking elsewhere for the problem. Symptoms for an intermittent spark misre typically show up under light load part throttle at cruising speeds.  Note: Fuel Fu el trims being over 10% directs you to a fuel  problem, and therefore the misre is less likely from spark.

No misres on cylinder number two

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

109 Bidirectional Testing Advantage

Scan Tool Live Data

Live Data and Bidirectional Testing are two ways to test a circuit without pulling out a voltmeter! If you look under  “Live Data” on the scan tool you’ll see columns of data made up of numbers and values. Better known as PIDS (Parameter Identication) you can use this information to  better help he lp diagnose d iagnose problem circuits.

Using PIDS Alone to Test Since the 906BT uses bluetooth I can bring the tablet to the  back of the vehicle and activate the actual back door  opener switch switch and look to which PID’s show “on” (versus (versus off) in the scan tool. If the hatch does not unlock (no sound when activated) but the back door open handle switch says “on”, I at least know the switch is ok and would start my testing in the other part of this circuit. Using PID’s saves me time by not having to manually test each part of the circuit.  Note: An indication that the Back Door Lock Assembly did not operatee (in addition operat addition to not hearing it click) would be seeing the Back Door Courtesy Switch stating “off, “ when trying to open the back door hatch.

Main Body Computer 

Back door opened when using the back door openproperly handle switch.

Note: Any time the Back Door Lock Assembly is in the unlock position the courtesy switch closes creating an “on” state on the scan tool.

Courtesy

 

Switch

Back Door  Lock  Assembly

Back Door  Open Handle Switch

 

110

Doing a Bidirectional Test Look under “Active Test” in the specic system to command comman d the specic specic computer module to activate activate a component you want to test bidirectionally. For example: On the 906BT under “Main Body” I clicked on trunk and  back door open. I selected several PID’s pertaining to the  back door circuit shown. Clicking “on” commands the  back hatch to unlock and open. If the hatch opened when using the scan tool, but not when using the actual back  door switch, it is most likely an Input Problem (switch part of the circuit). circuit). This also veries that the computer computer is good as well as the wiring that powers the Lock Assembly. This gives you a direction to start your pinpoint tests.

Rule doing Bidirectional Test: If component does not activate Bidirectionally Bidirec tionally look to Outputs Outputs (Computer, Wiring to component and Component). If  it activates with scan command, but not otherwise, look to your Inputs (switch and wiring) in general.  Activating Back Door Hatch using the 906BT scan tool.

Main Body Computer 

Inputs

Outputs

Courtesy Switch

 

Back Door  Open Handle Switch

Back

Door  Lock Assembly

 

111 11 1 Automotive Oscilloscope I nd the Autel MP408 Maxiscope works well with my 906 BT scan tool tablet as both are rugged and have a small foot print for sitting on a vehicle’s fender if needed. The tablet comes with an App built in to recognize the scope. Whats nice is it is battery powered by the tablet and it can record and play back voltages. This is great for  catching intermittent problems while driving. Click on the App and the scope screen opens. Here I show using two channels (of four) which is like having two voltmeters side by side. A scope that can record and playback the waveform is known as a Digital Storage Oscilloscope (DSO). Note:  An oscilloscope, voltmeter, amp clamp show actual data versus what the scan tool shows (which is processed processed data). When in doubt about the scan tool data, always check and believe believe the actual data using direct measurement.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

112 Toyota Crank Sensor Signal

What’s different about the scope is that it shows and What’s measures voltage against time. You hook it up just like you would for a voltmeter as there are two leads per channel. You can access the waveform just as you would on a standard PC tablet - just click on it.

     s        t       l       o        V       5 

Once a waveform is captured you can use your thumb and forenger to spread the signal (sideways), just like you would with a smartphone. Time

Toyota Cam Sensor Signal

Click on the scale line (to the left). Then drag the waveform up or down on the graph with your nger to move it.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

113 Toyota 4 wire COP combines ignition coil and igniter 

Ignition Coil

Igf 

Igniter  To Spark Plug

 

Crank Sensor 

ECM

Igt Cam Sensor 

When measuring signalstesting to cut start your by circuit in half. IfIgt/Igf  Igt and Igf signals are present then you know the ECM, Crank Sensor and Cam Sensor are good.

On older vehicles the Ignition Module (Igniter) that triggered the ignition coil was externally mounted and was separate from the coils. Most modern coil on plug (COP) systems incorporate the two into one COP coil for each cylinder. Some manufacturers like Chrysler have the igniter inside the ECM. So testing varies depending on the vehicle you are working on. On Toyota COP coils, the ECM takes input from the crank  and cam sensors and sends a trigger signal to the igniter via Igt. This momentary momentary signal causes the igniter igniter to cut the eld to the ignition coil primary circuit circuit inducing a much greater eld in the secondary coil - which then produces a spark. Igf is the feed back signal to the ECM letting it know that spark occurred. If not received, the ECM will turn off the fuel injector for that cylinder saving the CAT from over  heating.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

114

IGF

IGT

Scion xB at idle and ring number 1 cylinder COP coil over and over on the scope.

MaxiScope +B

Cylinder No. 1

 

IGT

 A   B

COP IGF   GND

Before condemning a COP coil, test the electrical connections connected to it.

Note: On Chrysler Chrysler vehicles use the scan tool test to trigger  spark (with a bi-directional scan tool). If this test shows spark then a no spark condition (without using the scan tool) is an input sensor problem.

•

Bac Backpr kprobe obe +B +B and GND with with a test test light. light.

•

Bes Bestt to use use an oscil oscillos loscope cope to to check check IGT and and IGF. IGF.

Use two channels of the scope to check these signals at the same time.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

115

Spark Tester  IGT

• With With the igni ignitio tion n key on, on, a manua manuall spark spark test test ccan an be  performed by taking an LED test light connected to the  battery positive p ositive terminal and momentarily touching the test light to IGT of the COP coil to see if it will create spark  one time. If it sparks you know the COP coil is good.

Using a Low Current Amp Clamp The unit can be used with a digital meter or an oscilloscope.

Zero Ze ro Me Mete terr

•

First First turn turn on the the uni unitt and zero zero out the readi reading ng on the the display.

•

Find Find the + and and - signs signs on the the side side of the the unit unit and clip clip it it around one wire with the + side pointed in the direction of wire going back to the power side of circuit.

In automotive automotive you typically use the dc settings and convert the voltage read on the unit into amperage. My example meter has two conversions. One for the 20 amp scale (Use 100 mV per amp) and the other is the 80 amp scale (use 10 mV per amp).

Example: On a 20 amp scale - say reading is 0.5 volts (500 mV). 500 mV divided by 100 mV equals 5 Amps. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

116 Current Ramping Ignition Coils On certain engines such as the V6 Toyota it is difcult to access some of the COP coils and would be extremely time consuming to do a swap test. Instead use an Amp Clamp to scope and test the amp ow on all coils in relation to IGT signal on number 1 coil. Then use the ring order to determine exactly which COP coil is  bad. Here, by looking at the wiring diagram for the 2013 Scion xB, the 15A Ign 2 fuse powers all 4 ignition coils. The fuse was removed and a jumper wire was installed in its place. The Amp clamp was clamped around the wire loop. The Amp clamp was set on the 20 amp scale and attached to the oscilloscope.

On the 20 amp scal scale e use 100 mV equals 1 amp.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

117

Firi Fi ring ng Orde Orderr 1, 1,3, 3,4, 4,2 2 Coilil mp Co mper erag age e

3

#1 Coil IGT

4

2

1

#1 Coil IGT

Notice the small peak voltage reading between cylinders. cylinders.off  The fuel injectors are powered the same fuse as the ignition coils and show they output approximately half an amp.

Looking at the green 2 volt scale (B channel) we see 1.1 volts on number 1 cylinder coil coil peak. This calculates calculates to 11 amps approximately. All coils appear to have the same value. Had one been drasticall drast ically y high or low then it may indicate it is failing. failing.

 Note: Keep in mind that if a factory coil had been replaced  by an off brand coil the value might be a little different and would still indicate indicate the coil is good.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

118

Expan and ded Time line to isolate signal nals

IGT

Coil # 1

Coil # 1 is good as are all the coils on the Scion. The initial rise of amperage is what to look for in a coil that is good. It should be a gradual increase. increase.

ood

If the amperage jumps straight up to begin with it is  possibly starting to short out and go bad.

Bad PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

119 Fuel Pump Current Draw Test Using the same low current amp clamp hooked to a digital voltmeter, look at the vehicle wiring diagram and determine which fuse powers the electric fuel pump mounted in the gas tank. In this example, I replaced the 20A EFI Main fuse with a loop of wire. Then attached the amp clamp around the loop of wire and set it to the 20A scale. Again zeroing the meter  setting prior to attaching the amp clamp. Starting the car and measuring the amp ow I got 7.6 amps of current ow through the pump. Use the chart below:

 Normal TBI = 2 to 5 amps (9-13 psi) Port injection = 4 to 8 amps (35-45 psi) Central Port Injection = 8 to 12 amps (55-64 psi) Service Manual Specications Service Specications for the Scion xB are 44-50  psi. I go by pump pressure assuming 45 psi. Which is just  below 8 amps for port po rt injection and looks good. Typically a bad fuel pump will run higher than specications. Yet don’t rule out a restricted fuel line due, to say, a clogged fuel lter. If amperage is lower than specication check for a bad fuel  pressure regulator or poor p oor electrical connection. conn ection.

100 mV per Amp or  0.1 Volt per Amp gives 7.68  Amps on the Digital Voltmeter 

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

120 Toyota Toyot a Stand Standard ard EFI Fuel Pump System

7.5 A IGN

 

20 A EFI Main

Crank Sensor 

EFI Main Relay

ECM MREL

Circuit Opening Relay

FC   ST STA A IGN Start

Fuel Pump

Note: Fuel pump can be turned on by using a bi-directional scan tool to access it.

The Scion xB, as well as many Toyota Fuel Pump Systems, use 2 relays to power the fuel pump. Unfortunate Unfor tunately ly the EFI Main Relay is internal to the Integration Relay. Connections to it cannot be easily accessed without disassembling the fuse box. The Circuit Opening Relay (Fuel Pump Relay) is internal internal to the Body Control Module which is hidden inside the dash. Therefore, test the inputs and outputs rst. This will eliminate elimi nate deeper tests that would require a lot of  disassembly time. Test at fuses, fuel pump, and ECM which the connections are a lot easier to get to.  Note: Power to the fuel pump is rst controlled by the ignition switch during the crank position. So a person is needed  behind the wheel to crank the engine, while another person

tests for power to the pump. Once the engine starts, the ECM keeps the circuit opening relay closed, as long as it sees an RPM signal via the crank sensor. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

121 Crank Cra nk Sensor Sensor Fr From om IG IGN N Star Startt

ST

ECM

40

30

20

#10

B 3

B+

2

 

1

C

Note: Maxiscope rated at 100 volts per channel and needs an attenuator  when measuring injector  injector  voltage.

D

Fuel Injectors Ground side switched through ECM

MaxiScope  A

No start condition and no RPM signal, when cranking engine, yet you have a check engine light that is on, check for a faulty crank position position sensor. sensor.

 ttenuator 20:1

Testing for an Open Fuel Injector Circuit •

Shown in example above: crank or start start engine and check for an injector signal on number 1 injector at the ECM. If you have a signal but no pintle hump the

injector may be stuck? A) No start (and no signal) with key on check for battery voltage at same location? B) No Voltage at A now check for battery voltage at B. C) No voltage at B now check for battery voltage at C. D) No Voltage at C now check for battery voltage at D.

Pintel hump shown here proves that injector opened mechanically.

The open is right before the last place you had no voltage. Repeat the process for other injectors.  Note: No spark on one cylinder can cause the ECM to turn off the injector (protecting the CAT). To verify a spark   problem turn engine off and cycle the key on and then off.

Crank the engine while watching watching for an injector signal to show initially but then to disappear. If this happens troubleshoot spark before moving on to fuel injectors. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

122 Gas Direct Inject Injection ion (GDI)

Fu Fuel el Pu Pump mp Speed Spe ed Mod Module ule

+ 12V

ECM Crank Cra nk Sen Sensor sor

High Hig h Pre Pressu ssure re Sensor Fuel Fuel Ra Rail il GDI Inject Injectors ors

High Pressu Pressure re Pump

Fuel Tank

Low Pre Pressu ssure re Sensor

Lo Low w Pr Pres essu sure re Fu Fuel el Pu Pump mp

Cold start driveability may occur due to the intake valves collecting collec ting carbon deposits on this system. Use a borescope to inspect the valves as cleaning may be necessary.

GDI Fuel System with PWM Fuel Pump On a GDI System gas is directly injected into the combustion chamber under high pressure. There are two fuel pumps in this system. It uses a standard low pressure fuel pump mounted in the gas tank. A second high pressure fuel pump is mounted on the engine and driven by direct contact with the engine’s camshaft.

Note: Most systems can still run with an inoperative high pressure pump, but will lack good acceleration, acceleration, so check pump pressure (upwards of  1500 to 3000 psi) under raised RPM.

Unique to this system is a pulse width modulated modulated (PWM) low pressure fuel pump. Duty cycle of the pump is driven  by a Fuel Pump Module. Control for the duty cycle is controlled by the ECM. A fuel pump current draw test cannot be done directly directly on this system. system. Rather compare compare the duty cycle on the scan tool (or scope) while watching the fuel pressures during your diagnosis. The high pressure side should be low at idle but increase with engine RPM. Use the scan tool to further pinpoint problem injectors as

individual injectors can be turned off as well as other tests, depending on the manufacture’s specic system.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

123 Controlling Power ON Power Side Switching

Pull Up Circuit

Note: Since GDI Injector wiring is hard to reach on the engine it best to backprobe the injector  wiring at the ECM.

 

Ground Side Switching

Pull Down Circuit

What controls the output device? I prefer to call it Power  or Ground side switching. As calling it a Pull Up or Pull Down circuit does not address switching directly. Unique to GDI Systems is that the fuel injectors are both  power and ground side switched by b y the ECM at the same time! When using the scope to check voltage, use a separate channel for each leg of the injector you are testing.

12 mps

Add an attenuator as voltage can spike up in the 200 volts range. Careful Careful to avoid electric electric shock while the engine is running (Wait 5 minutes after the vehicle is turned off to allow capacitors in the ECU to self discharge before touching a connector). Using an amp clamp and a scope is a good test of the injector inject or ring as the individual individual injectors draw 10 to 12 amps initially and then drop to a couple of amps. They are

 better known kn own as peak and hold injectors.

Inje In ject ctor or Curr Curren entt PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

124 Relative Compression Test A simple and fast way to determine if a cylinder has low compression is to do a Relative Compression Test (especially when spark plug removal is hard to do). By adding a second channel you also pinpoint pinpoint which cylinder  has the problem. The low compression cylinder will have less resistance to starter current and show up on the scope when compared to other cylinders. 1. Connect tthe he low current current 695 Amp Amp Clamp to to channel A. A. Connect the channel B leads to the number 1 cylinder IGT signal output from the number 1 ignition ignition COP coil. 2. Attach th thee 695 clamp around around the negative negative starter starter cable with the negative side pointed toward the batteries negative  post. Positive arrow (shown) should point away from the negative battery post. 3. Set the Amp Cla Clamp’s mp’s voltage voltage setting setting to the 80 amp DC scale which equates to 10mV per amp. 4. Zero out the the Amp Amp Clamp. Clamp. 5. On the sco scope pe set Channel Channel A to 2 volts volts DC and set set Channel B to 20 volts DC. 6. Set time to app approxim roximately ately 100 mS per divisio division. n. Disable the ignition or fuel injection system to prevent the engine from starting. •

On GM, GM, Ford Ford or Ch Chrys rysler ler h hold old the the gas pedal pedal to the the oor  (clear ood mode) while cranking the engine.

•

On ve vehic hicles les like like Toyota Toyota use use the the scan scan tool tool to to cut fuel fuel to to all cylinders.

7. Crank engine over for a few seconds while recording the data. Adjust the horizontal scale, if necessary, as there should be one hump for each cylinder (at least 4 humps for a four  cylinder engine).  Note: The hump corresponding to the bad cylinder will be very low or essentially be nonexistent.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

125 Use Us e ct ctiv ive e te test st mode an and d sc sco ope mode ode at the sa same me time time

To Swit Switch ch ac ack k and and fo fort rth h  etw  etwee een n fu fuel el cu cutt sc scre reen en and and sc scop ope e sc scre reen en Firing Fir ing Order Order 1,3,4, 1,3,4,2 2

1

4

2

1

 ll cyli cylind nder ers s have have good good comp compre ress ssio ion n - re reco cord rded ed duri during ng engi engine ne cr cran anki king ng

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

126 Use Relative Compression Test to check for correct valve timing Since spark timing is triggered off the engine’s camshaft  position, a jumped timing chain, c hain, or a stuck retarded VVT camshaft, will cause spark to occur other than at top dead center of the compression stroke (VVT system that uses intake camshaft only). Keep in mind that the Amp Clamp needs to be attached in the correct direction. See attached images.

Correct Amp Clamp direction on battery cable and correct valve timing during engine cranking.

Incorrect Amp Clamp direction on battery cable with correct valve timing.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

127 Cam Crank Correlation Method of checking Timing

Another method of checking Another checking for correc correctt cam timing timing of the engine is to compare the cam sensor signal to the crank  sensorr (count number of crankshaft senso crankshaft peaks in relation relation to a specic camshaft peak). This only works if you have a known good pattern of the two together. together. Sometimes Sometimes you can go online and download a pattern that someone someone else has taken of their vehicle. vehicle.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

  

128 Variable Valve Timing (VVT-i) Note: Those vehicles that also use VVT on the exhaust cam incorporate more controls not shown here.

Crank Position Sensor  Mass Air Flow Sensor 

E C M

Throttle Position Sensor  Engine Coolant Temp Sensor 

Duty Cycle Controlled

Vehicle Speed Sensor 

VVT Controller  (Camshaft Timing Gear Assy)

OCV

Intake Camshaft

ECM OCI-

OCI+

MaxiScope

 A

OCV

TIP: Engine stalls when doing a UTurn? Check oil level might be too low causing VVT camshaft timing. to lose

A VVT system adjusts intake valve timing to improve driveability. This system eliminates need for an EGR  valve. Engine oil pressure turns the VVT Controller to adjustt the valve timing which is controlled by the oil adjus control valve (OCV). Inputs to the ECM determine the duty cycle output to the OCV valve. Correct oil viscosity needs to be maintained for this system

Note: Use scope or digital multimeter to check duty cycle.

to properly operate. When troubleshooting always check  the oil quality rst.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

129

 mp  m p Clamp set to 100 mV per mp

ECM

 Amp Clamp

OCV

 Amperage to OCV valve increases while activating it bi-directionally with the scan tool.

Scan Sc an Tool ool ctiv ctive e Tes estt Mo Mode de

•

Use the the scan scan tool to test test the system system by activat activating ing the the OCV valve. If engine stalls you know the OCV valve output circuit and ECM are good. Also as duty cycle increases so should amperage to the OCV valve as shown.

If system tests good using the scan tool but won’t activate activate while driving the vehicle, problem is with one of the input

sensor circuits to the ECM.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

130 Electronic Throttle Control

Use service manual information for specic wire voltages to pin point specically where problem is, based on code generated. generated.

Throttle Throt tle Posi Position tion Sens Sensors ors

Better known as “Drive by Wire,” the throttle is electrically driven.. In this system the ECM has two separate central driven  processing units u nits along with VTA and VPA for redun redundancy dancy should one system fail. One fail safe mode example: If the throttle valve in the bore is manually held open by an

obstruction,, the problem obstruction problem will be detected by the ECM and it will turn off the engine. A check engine light will come on in the dash and a code will be stored in memory. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

131 • Initia Initiall check check is to check check in in the thro throttl ttlee bore bore while while watching the throttle valve open and close (key on engine off). Press the accelerator pedal and listen to the operating sound of the running motor. If friction noise exists replace the throttle and motor body assembly. • If the throttle throttle control control motor motor does not operate operate,, measure measure the resistance of it. In the example shown, you would disconnect the connector at the throttle position sensor and measure the amount of resistance from M+ to M-. If not  between .3 to 100 ohms replace the unit. Best to use scan tool live data to verify the problem area, along with the specic specic code generated. generated. Refer to the service manual for any additional tests needed. heck heckin ing g fo forr code codes s

VT 1 and and VT 2 vo volt ltag ages es show show work workin ing g pr prop oper erly ly

Sc Scan an Too ooll Li Live ve Data Data

Though the scan tool live data uses percentages and not voltages, you can still use it to see if the system is working. While watching the percentages, as you step on and increase the accelerator pedal, the numbers should increase. You can switch to graph mode on the scan tool and watch for any drop outs in the signals. After checking checking the scan tool information information and nding a code or a drop out in live data, check for voltages in the specic  problem circuit to help pin point the problem.  Note: A common repair is to clean the throttle valve area. Careful that you rst turn off the ignition switch prior to cleaning it. Don’t spray in the bore as it may leak into the electronic parts and short them out. Rather use carburetor  cleaner on a rag and wipe the throttle bore instead.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

132 Smart Stop Technology and Electronic Throttle Integration Above 5 mph when the driver presses the accelerator, and  brake pedal at the same time, the ECM reduces the engine  power by decreasing the throttle valve. This protects the driver from unintended acceleration. The stop light switch is integr integrated ated into the vehicles vehicles ECM via the CAN system by way of the vehicles skid control ECU (also integrated with the traction control system). Therefore Theref ore a lack of power could happen happen if the stop light switch were to stick intermittently. With this knowledge you can use the scan tool to help in diagnosis. diagnos is. Use the scan tool’s record feature feature to view Live Data.

Using Scan Tools Record Feature • In Live Live data, data, select select the stop stop light light switch switch (PID), (PID), thrott throttle le valve (PID), accelerator position sensor (PID) and RPM (PID) to view conditions, while driving driving the vehicle vehicle to see if  the stop light switch comes on when it is not suppose to! • If the the switc switch h shows shows “on” “on” (whe (when n your your foot foot is not on on the  brake pedal) then troubleshoot the stop light switch circuit in more detail.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

133

Example: Using the Record Feature on the 906 BT Scan Tool

Brake and Gas applied same time - see Throttle decrease In three of the ve PIDS shown, switching to graph view, one can see the ECM reduced the throttle angle when the  brake and gas pedal were depressed at the same time, above 5 mph. Using this recording feature is important when you have an intermitte intermittent nt problem. The above example how the brake lightcontrol switch is a shared input betweenshows the braking and throttle system. Assuming you had an sticking switch, without this knowledge, one could have easily replaced the throttle  body when the real problem was with the brake light switch! Keep in mind this is just one example! Modern vehicle systems syste ms are integrated. integrated. Use the repair manual to learn as much about each indiv individual idual system, system, that you can, prior to troubleshooting the vehicle.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

134 Toyota Key off Evap System

The Evap System keeps fuel vapors from venting to atmosphere thereby decreasing pollution. Note: A check of mode 6 Evap Monitors will indicate if monitors have run and if they are good or not. Use the generic side of the scan tool to access them.

• Purge Purge valve valve is is normal normally ly close closed d so fuel fuel vapor vaporss are are collected collec ted in the canister and excess pressure is vented out the vent valve which is normally open. • Shown: Engine running (and warmed up) purge valve opens and stored fuel vapors are pulled out of the canister  and burned in the engine. System Self Test Monitors 1) ECM monitors monitors the fuel fuel tank pressure pressure sensor sensor (FTP) (FTP) for  negative pressure while engine is running. If no negative  pressure then the ECM temporarily closes the vent valve and looks for a 3.0 mmHG drop, or more. If this does not happen, the ECM assumes a bad purge valve and triggers a

P0441 code. 2) 5 H Hour our Soak Test Test

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

135

The 5 hour test will not run unless the vehicle has been driven for 10 minutes and the fuel tank is less than 90 percent full.

Mode Mo de 6 Mo Moni nito torr Stat Status us

Five hours after engine is turned off the ECM runs a series of tests on the evap system (if fuel is very hot it may take longer to start the test). Basically the vent valve is closed and the vacuum pump is turned on. If no leaks in the system, the pump should drop  pressure in both tank and canister to a certain level. Lastly the purge valve is opened via duty cycle to relieve the pressure and the ECM watches the FTP sensor for a  pressure increase. This is a test of o f the purge valve itself. If  all works ok the ECM sends a “system ok” to the evap monitor status. Leak codes are diagnosed using a smoke machine that  produces no more than ½ psi of pressure (a machine that  produces any higher pressure may damage the internals of  the evap system). Make sure you manually block the vent valve, when smoke testing from the purge port opening, (unlike some other  manufacturer vehicles where their vent valve seals the system completely), as the vent valve in this system does not fully close when energized. If you don’t block it off  smoke will appear under the gas cap where the vent opens to atmosphere and you will swear you have a bad gas cap!

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

136 Use a bidirectional scan tool to bypass the 5 hours and run the self test to verify verify any problems problems with the system. system. The 906 BT is capable of running the Auto as well as the Manual Self Test on the evap system. system. Unfortunately, Unfortunately, it is not perfect, so disregard using the graph troubleshooting charts shown in the service service manual, as they most likely work well with the factory scan tool but not the Autel, in

May take 5 to 15 minu inutes to run uto

my experience. Just use the test modes as a go/no go method of testing the system.

Use as a go/no go test

Manu Ma nual ally ly cl clic ick k th thro roug ugh h is fa fast ster er

Good Go od sign sign syst system em ha has s no le leak aks s

Wat atch ch fo forr pr pres essu sure re ch chan ange ge du duri ring ng te test st (if (if no chan change ge may may ha have ve a ad vacu vacuum um pu pump mp?) ?)

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

137 Troubleshooting the Evap System Live Live Data Data Mode ode

The rst check should be to have a good working gas cap. Replace it if in doubt. The purge valve is also easily accessed and can be checked by using a hand vacuum  pump, and electrically by b y using an ohm meter. Having a good canister fuel pressure pressure sensor (FTP) is of the most importance as if it does not work it will be difcult to tell if the system works as it should. A quick test is to watch the vapor pressure in live data as the engine warms up. Once the purge valve turns on the  pressure should change slightly as purge ow duty cycle  percent increases.

Bi-directional Bi-direc tional Test

You can further test it by activating the vent valve and watch the pressure in the syste system m drop. Be careful not to drop more than 3 kpa. So turn off the “vent on” mode once 3 kpa is reached else you could collapse the gas tank (if gas cap relief valve does not work). Alternately, you can hook a DMM to the Vout and ground on pin 3. Then smoke test the purge line with the “vent on” energized, using the scan tool, and see a voltage change (increase) (incr ease) as one half pound of smoke pressure pressure is applied. applied. Pinpoint tests can be done by hooking a voltmeter to specic circuit pins either at the ECM or the Leak  Detection Pump. Then use the scan tool to operate the specic circuit using manual mode.  Note: If you get 5 codes at once (P043E, P043F, P2401, P2402, P2419) and get no change in vapor pressure though the FTP sensor tests good, the vacuum pump is most likely faulty fault y (even if motor runs). Fix is to replace canister and leak detection pump as a unit.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

138 Modern cars use Multiplexing

Horn

Bulb Solenoid Switch

Signal Horn

ECM

Switch

ECM

Bus Comm Line

Bulb Solenoid

A multiplex circuit uses one ECM to send a series of coded voltage signals to another ECM through a singlee wire saving on wiring. These data packets singl may tell the receiving ECM to: • •

Turn Turn on a ho horn rn Ener Energi gize ze a bu bulb lb

•

Acti Activat vatee a so sole leno noid id

High Speed (H.S.) Can Primer

Most cars now days use a 2-wire H.S. Can System. My 2013 Scion xB has 10 computer modules (ECM’s) all talking to each other on the can 2-wire  bus communication (data) line. Some Lexus vehicles vehicl es have 30 modules. Mercedes have 50 modules!! So being able to diagnose modules diagnose the system system quickly is important.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

139 Combo Meter Module  20

JUNCTION CONNECTOR 7

8

4

 

Pins 6, 2, 4 and 7 are connected to Can High. Where pins, 14, 3 and 5 and 8 are connected to Can Low.  4

6

2

3

 20

DLC  ABS Module

PCM Module

Basic Can System This shows a reduced example of a CAN Bus line. All modules are connected up in parallel using a Junction Connector.   Individual wire connections (indicated (indica ted by the circle dots) become totally totally open when the Junction Junction Connector is removed. removed.

Can Main Bus Line 120

CAN MAIN BUS 7   8

The DLC (Data Link Connector) taps into the Main Can Bus Line. The line consists of Can High and Can Low wires and two terminating resistors connected in parallel.The two resistors combine to create a resistance of 60 ohms when measured at DLC’s pins 6 and 14.  Notice I did not include the ABS module in the

Can Low

14

 

6

Can High

4

example here. That is because it is not part of the  

5

main bus line.  Doing an ohm check at the DLC only checks the main bus line and the DLC wires connected to it.

120

DLC

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

140

Sub Bus

3 2

 

Sub Bus The Sub Bus is also connected in parallel to the main bus  but it does d oes not have a resistor in its circuit. If you yo u pull the  back off the Junction Connector Con nector the Sub Bus would wou ld be disconnected from the main bus as shown here. Using an ohmmeter and measuring resistance between pin 2 and  pin 3 you would nd the resistance to be very high if not no t innite. If you measured anything below say 1 meg ohms then most likely you have a short circuit in the module. Point:

Can High

 

Can Low

This circuit needs to be checked individually as it is not   part of the main bus. b us.

 ABS Module

3 2

Can High

 

Can Low

 ABS Module

To check the sub bus wires with an ohmmeter one has to disconnect discon nect the module connector connector and ohm check each wire separately (Can High and Can Low) end to end. They should have low resistance indicating continuity.

With a Can High Speed Bus System you can have as many as 13 modules connected up to the Main Bus Line. With two modules having terminating resistors (connected (connec ted directly in the main bus line) that leaves 11 modules connected up by sub bus. Having nothing else  but an ohmmeter one would have to do d o a lot of checks on the bus line. That's assuming you can nd each module which is buried deep under a lot of interior and exterior  molding moldin g in the vehicle!  Note: Keep in mind a Gateway is required to add more than 13 modules to the network and their bus line cannot

 be directly checked ch ecked doing an ohm measurement at the DLC.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

141

Can Bus Network with Junction Connectors Here it is what Scion shows in one of  their service service manuals. manuals. It has 10 computerr modules and 2 Junction compute Junction Connectors - plus the Data Link  Connector (DLC).  Note: Some Scions have an Accessory Bus Buffer. This vehicle does no have one.  A key point here is that there ther e are not  one but two Junction Connectors Connectors. Since it is hard to nd each module in the car, by accessing the Junction Connector Connect or it will make it much easier  to test each of them. More on this later.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

142

Digital Digit al Multimeter Multimeter use with CAN Having a multimeter allows you to do some quick checks on the can bus. Measuring both Can H and Can L for  voltage gives you a rough check for shorts to power and ground. After all doors are closed closed and ignition is turned off  you can watch when the bus goes to sleep as the voltage drops to zero. This may take 15 to 30 minutes or so? After  the bus goes to sleep you can do several ohm checks as well.

Powerprobe Cat-IV Digital Multimeter 

Some vehicles need reprogramming, if the battery is disconnected, so the advantage here is you don’t have to disconnect it before doing your checks.

 Y  You ou need a Bi-Directional Scan Tool Having a good quality bi-directional scan tool that scans all the modules on the vehicle is a must for diagnosing Can Signals. Pay attention not only to codes but also what moduless the tool can communicate module communicate with. This will be your  rst clue as to what module to start diagnosing rst. It is very easy to overlook overlook this depending on your diagnostic diagnostic machine.

 Autel MK-906 BT accessing  AllData wiring diagram via wi

When using the Autel MK 906 BT it skips right over any modules that don’t communicate when checking for codes! They won’t show on the screen. You can see it skipping a module, as it rst will try to access and show it. Make a note to which communicate and which do not. Keep in mind some cars simply do not have a specic module. The Scion xB does not have an immobilizer. immobilizer. Afterward, Afterward, check  the wiring diagram to determine which modules the vehicle has, for this purpose. If in doubt, you can use the scan tool to select an individual module to see if the scan tool communicates with it or not.

Doing a full system scan, the  Autel shows immoblizer for only a few seconds seconds.. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

143

Pay attention to codes if all modules seem to be showing up on the scan tool  U Codes After doing your initial scan of the vehicle, any U codes are an indication that you may have a communication  problem. Make sure you save the codes before deleting them to see what hard codes come back when re-scanning the system. When checking for any codes, if you nd a U code, you should start your troubleshooting with the Can Communication System rst.

History Codes Determine Deter mine if the codes are current or history history codes. If they are history codes you may have an intermittent problem? If they are not happening currently, you can’t troubleshoot the system until they become current codes again.

Take advantage of what the scan tool can do Try to recreate the problem before inspecting a connection as once you touch that connector connector you may accidentally accidentally have xed the issue and never know you did it! Loose connections are a common cause of electrical  problems. If you suspect an a n intermittent problem causing a loose connection: 1. Try acti activating vating the the problem problem circuit circuit using using the scan tools tools  bi-directional features.

While watching the scan tool, wiggle the AC pressure sensor  wire to check for an intermittent disconnection.

2. Switc Switch h to Active Active mode mode (turn (turn on record) record) and monitor  monitor  inputs and output information while gently wigging wiring connected to the circuit. Any change in the data  points to the problem area. 3. Final Finally ly disconnect disconnect all all connections connections related related to sensor sensor and and module involved involved and inspect inspect them making sure they

reconnect rmly.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

144

Rule: Any Time you have a U code and/or a module that won’t communicate with the scanner do a quick check of the Can Bus System using a breakout box and you DMM.

 Note: Don’t be fooled if the car has a “gateway” (more than one can network) as a breakout box will only check part of the total network.

Using a Breakout Box Pin 6 Can H, Pin 14 Can L

One of the advantages of using a breakout box is that you

Pin 4 and 5 are grounds

don’t spread the terminals of the DLC connector with your  test leads. The other end of the box allows you to connect your scan tool at the same time. Each terminal has an LED light beside it to let you know if  it is active. Lights at pin 16, 4 and 5 lets you know you have battery power and good grounds to the unit. This is especially helpful when your scan tool will not communicate with the vehicle. If a light is not on, you now know the problem is with the vehicle wiring and not your  scan tool. When there is activity on the bus, lights (at pins 6 and 14) on the box begin to blink. Though not as good as checking a scope pattern it does tell you there is activity on the bus. You also have easy access to power and ground. With the vehicle battery disconnected doing a resistance reading from either Can H or Can L to ground gives you a quick  check to see if the bus is shorted to ground (should not be less than approximately 200 ohms).  Next check from either Can H or Can L to power terminal having low resistance. A resistance reading below approximatel approx imately y 6k ohms would indicate a short to power. It is always a good idea to hook the breakout box to the

DLC rst prior to using your scan tool. This way you can test for any reverse polarity problems that may damage your expensive expensive scan tool prior to using it. PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

145 A Digital Multimeter (DMM) voltage reading will look different from what you will see on an oscilloscope. oscilloscope. If you see major difference difference in voltages, voltages, from what is shown in the pictures below, you have a problem that needs to be investigated.

Oscilloscope Example: Can High 2.5V to 3.5V

2.5V Base line

Can Low 1.5V to 2.5V Bus Fully Fully Awake at 2.5 V Volts olts Looking at the scope, when the key is rst turned to accessory access ory mode, on some vehicles, vehicles, you will see approximately 1.8 to 2.0 volts on the bus base line, when looking at Can H or Can L to Ground. Once the key is turned fully to the “on” position you will see 2.5 volts as shown on the graph above. Turning the key off the bus starts to go to sleep around 1.7 volts. And is fully asleep when voltage reaches zero.

Can High Voltage DC 2.6V Fully Awake

Bus Voltage using a DMM Meter  When using a DMM on DC volts you will get an average voltagee compared to what the scope is showing. Still the voltag meter is helpful is determining that the bus is functional. And a short or an open would affect the voltages drastically.

Can Low Voltage DC 1.5 V Fully Awake

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

146 AC No Communicate

Scanning shows one modul Scanning module e does not communicate 1. Discon Disconnect nect the connector connector from from the module module in question question and connect an ohmmeter to both the Can H and Can L  pins of the connector. This measures the sub bus (branch line) all the way back in parallel with the main  bus. The resistance reading should be 60 ohms.

DLC

2. If the resis resistance tance reading reading is approximatel approximately y 20 percent higher or lower than 60 ohms (where it was 60 ohms measured at the DLC) you then have a problem with the sub bus branch. 3. Discon Disconnect nect the Junction Junction connector connector and ohm out out each Can wire, end to end, separately to check for an open  branch. 4. If all go good od then check check power and ground ground on the module. module. 5. All pri prior or checks are ok then replace replace the the module. module.

Alternate Voltage Method: If voltages are not super high or low, but not correct either, then disconnect disconnect suspected suspected module and see if voltages voltages  become correct? They Th ey are now normal, replace module.

In the above example the AC  Amplier sub bus branch lines were measured to be 60 ohms. It was found the module was bad after 

 Note:

checking for a good power and ground on the module.

Can L and should read 120 ohms. If reading is anything other than approximately 120 ohms then replace module.

Any module with a termi terminatin nating g resistor resistor can be checked after disconnecting it and using an ohmmeter to measure the resistance in it. Measure pins that connect to Can H and

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

147

Scanning shows two or more modules do not communicate Open Circuit

If two or more modules do not communicate, (one or more U codes are present) when doing a scan, and voltages appear normal, then check the main bus for a open circuit. A quick check would be to do a resistance reading of the DLC at pins 6 and 14 after disconnecting the vehicle  battery. •

Read Reading ing should should be 60 ohm ohmss

Say you read 120 ohms. Then one of the terminating resistors is missing from the circuit indicating a faulty bus line or possibly a bad module that contains the resistor.

120 DLC

Knowing that say the Power Steering Knowing Steering ECU module and the Combination Meter ECU module are not communicating, gives you a direction on what half of the circuit is open.

Split Half Search If the scan tool did not communicate at all you could do a Split Half Search to cut your testing time in half. In this case you would: 1. Discon Disconnect nect the Can Center Center Junction Junction Connector Connector and measure Can H and Can L on the lower half of the circuit. A resistance reading of 120 ohms would indicate indica te that the lower main bus was intact. 2. Reconnec Reconnectt the Can Center Juncti Junction on Connector Connector and disconnect Can LH Junction Connector, which allows you to measure the upper half of the bus. Measure one Can Bus line at a time. 3. From here you cou could ld disco disconnect nnect the Combinati Combination on Meter  Module and measure only the Can H bus line on the left hand side of the circuit, right before the Yaw Rate Sensor module, going to the upper left hand edge of the Combination Combin ation Meter Module. An open here would eliminate elimi nate the right half of the upper circuit and narrow you search down to four modules. Then continue continue with this Split Half Search method until you found the  problem.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

148 Normal H. S. Can Waveforms

Time Setting measures horizontally Normal Can High (red) and Can Low (green) waveform at 50 microseconds per division

Normal Can High (red) and Can Low (green) waveform at 50 milliseconds per division Voltage Setting measures vertically

Normal Can High (red) and Can Low (green) waveform at 5 miliseconds per division PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

149 Using an oscilloscope to check the Can waveform Using a scope adds to your diagnosis of Can circuit  problems. When using a scope with two channels c hannels you can view the Can H and Can L waveform at the same time. They should mirror each other.

Problem with an open resistor Problem resistor is that the scope pattern may look the same. You need to do this test early in you diagnosis. Still it could be a 60 ohm reading as the open circuit could be in a sub bus branch.

Open Terminating Resistor  Use the scope to check for an intermittent signals Hook up an oscilloscope to measure Can H and Can L signals to ground at the DLC (use a breakout box). Watch the scope patterns for several minutes. Look for  any glitches in the patterns, patterns, especially especially when a pattern pattern does not repeat.  Note: On some vehicles, v ehicles, Chrysler Ch rysler for example, have individual indivi dual connectors connectors on the back of the Junction Junction Connector Connect or where you can disconnect modules from the can bus at one location. Disconnect and reattach them one at a time while watching the oscilloscope, (until the glitch/bad pattern disappear), to nd out which module is causing the problem.

Faulty Pattern as upper does not mirror lower pattern

Depending on the circuit fault there are several different waveform patterns that will give you a hint of the type of   problem. From here you would switch to another method of  testing (explained in this publication) to narrow down where the problem is.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

150

Checking the 5 volt reference circuit In addition to checking power and ground on all modules that do not communicate, both the EFI module and the ABS module will typically typically have a 5 volt reference reference signal to  power sensors. Having a shorted 5 volt signal can shut down the module and not allow it to communicate. So make sure you check it  before replacing the module.

When the “Check Engine” light does not light up, when rst turning the ignition on, can be good indicator there is a  problem with the 5 volt reference circuit.

Indicates 5v reference is most likely ok

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

151

Can Signal Direction The problem here is that with the CAN Bus the signals are multi-directional!  Each computer module can be sending a signal to another computer (or several computer  modules) or receiving a signal from another computer (or  several computer modules on the Bus.

You cannot merely back probe Can lines at the module with either a voltmeter or an oscilloscope to see if the module is putting out a signal. The signal showing showing could  be coming from another a nother module on the bus. The service manual will have you do several process of elimination checks. You rst disconnect the sub bus at both ends (from module and main bus) then check the resistance of the wires, both CAN H and CAN L. If the wiring is good your next step would be to check the module for power and ground. If all is good then you replace the module. Yet without a denite denite failed resistance resistance check on the module, how do you know that the module is bad? Key here is that a scan tool is required. You use it in combination with your ohmmeter checks, after  disconnecting the Junctions connectors, to determine where the problem is. You need the scan tool to rst point out a missing module. After that you would check wiring and power and ground to the missing module. Then you can safely condemn it.

PRACTICAL AUTOMOTIVE ELECTRONICS ELECTRONICS

 

152 Take Care when Replacing Computer Modules Most newer vehicles have an immobilizer system which is coded to the key and/or key fob. The vehicle will not start unless matched correctly to the correct code. A blinking light on the instrument panel will indicate the system is armed. If the key or ECM is replaced, the car will not start unless the old code is erased and the new code input into the vehicle’s immobilizer module. In addition to the key and immobilizer immobilizer code, the vehicles VIN needs to be written into the new ECM or else the vehiclee may fail to pass the states emission vehicl emission inspection. inspection.

The Autel 906 BT can rewrite the VIN number to a new or used computer  module on some vehicles.

The Autel 906 BT can do some of the aforementioned on some vehicles. It can clear and rewrite new key codes and VIN numbers into some new and used computer computer modules (it just depends on the vehicle, make and year). Keep in mind the Autel can only input info (recongure sometimes called coding) on like computer modules. It cannot rewrite the software.When buying a used computer  module make sure to match it up with the same part number of the unit you are replacing or else you may have to have the vehicle towed to the dealership where they can reprogram repro gram the module to work with your vehicle. vehicle. Tips: Some Fuel Injectors need to be coded before before install. Replacing most GM computer modules require  programming using a J2534 Vehicle Communication Interface box, a laptop computer, an online subscription. •computer On ssome ome vehicle vehicles s you youofcan get atoprepr prprogram eprogr ogramm ammed ed online, instead trying it yourself.

Replacing a key fob requires old wireless key codes to be cleared and then new ones input into the door  control receiver module. Note: Save the old module as the scan tool, on some models, can pull the VIN number and save it and then input it to the new module, once installed.

Caution:

• On ssome ome vehicle vehicless you you may need two keys minimu minimum m to recongure their computer module or program keys. • On so some me Chrys Chrysler lerss you will will need need to get get a 4 digit digit pin pin number from Chrysler to recongure their module. • On so some me Toyot Toyotas as you you only only need need to use use a jump jumper er wire wire at the DLC to recongure their computer module. module. After programming, most modules need an initialization done. For instance, whenever you replace a PCM, crank  sensor, cam sensor, timing chain set on a GM you must do