Automotive engine electronics : How to diagnose and repair the automotive computer control system

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Automotive Engine Electronics

How to Diagnose and Repair the Automotive Computer

Control System

by Dr. Robert C. McElroy

Second Revised Edition

Accuracy Publishing, Homestead, Florida

photo by Rick Bernskoetter

Bob McElroy at the wheel of his Hilborn Fuel Injected Corvette at an SCCA autocross.

Note video camera attached to windshield.

Published by:

Accuracy Publishing Co.

Post Office Box 514

Homestead, FL 33035-051 4

Corvette Cover Artwork

Compliments of:

Micrografx Corporation

I

1511

Bob McElroy

All rights reserved. No part of this book may be used or re￾produced or transmitted in any form or by any means,

electronic or mechanical, including photocopying, record￾ing or by any information storage and retrieval system

without prior written permission from the author except in

the case of brief quotations embodied in critical reviews

and articles.

Copyright 1987,1988 by Robert C. McElroy, Ph.D.

First Printing 1987

Second Printing 1988, revised

Third Printing 1988, revised

Printed in the United States of America

Library of Congress Cataloging in Publication Data

McElroy, Robert C.

Automotive Engine Electronics

Understand, Diagnose & Repair: Fuel, Ignition

& Computer Control Systems

1. Automotive Electronics--Computers, sensors, etc.

2. Electricity and Electronics--Computers, sensors, etc

3. Diagnosis--Computers, sensors, etc.

4. Mathematics--Computers, sensors, etc

I. Title

ISBN 0-929603-37-0 Softcover

SECTION I -- Sensors & Systems SECTION II -- Driveability Diagnosis

TOPIC PAGE

Table of Contents 3

Objective 4

Foreward 5

Introduction 6

About the Author 8

Background of Today's Automobile 9

Electrical & Electronic Terms 11

OHM'S Law 16

Series Circuits 18

Parallel Circuits 20

Series Parallel Circuits 2 1

Diodes 22

Despikeing and Clamping Diodes 24

Transistors 25

Point Style Ignition Systems 26

HE1 -- High Energy Ignition 29

EST -- Electronic Spark Timing 3 1

Distributorless Ignition Systems -- CI 33

CCC -- Computer Command Control 35

EFI -- Electronic Fuel Injection 38

PFI -- Port Fuel Injection 40

Transition -- fuel to electronic systems 43

Throttle Position Sensor -- TPS 44

Temperature Sensors -- CTS & MAT 46

Manifold Absolute Pressure -- MAP 47

Electronic Spark Control -- ESC 48

Mass Air Flow Sensor -- MAF 49

Eshaust Gas Recirculation -- EGR 50

Idle Air Control -- IAC 53

Vehicle Speed Sensor -- VSS 54

Evaporative Emission Control -- EEC 55

TOPIC PAGE

Driveability Diagnosis Philosophy

Systems Approach to Diagnosis

Electronic Control Module -- ECM

ALCL Terminal Circuits

Scanner Use

Integrator & Block Learn

Scanner Error

Diagnostic Procedures

Digital Multimeter -- DMM

Jumper Wires & Connectors

Computer Harness Adaptive Tester

Diagnostics & ECM Voltage Checks

Continuity Tests

CHAT Basic Test Procedures

CHAT Advanced Testing Procedures

Advanced Circuit Testing

ECM Codes

Open & Closed Loop

Fuel Injector Balance Test

SECTION Ill --

SELECTED

ECM VOLTAGES &WIRE DIAGRAMS

Which can be read with CHAT.

Note: CHAT will interface BCM and GMP4 design

ECMs. BCM and GMP4 circuits have not been included

in this publication. CCC and EFI systems incorporating

"edgeboard" connectors were not included.

CHAT is covered by U.S. Patent No. 4,690,475 and is available from Diagnostic Products Co.

P.O. Box 1136, Homestead, Fl. 33090

Diagnostic Products Co. is the Electronics Subsidiary of Spectra Investments Ltd. Inc.

Objectives of this manual:

1. Provide a comprehensive general explanation for electronically

spark controlled and fuel injected engines manufactured by GM.

2. Provide specific information for the use of ALCL "scan" tools.

3. Provide specific information for the use of "CHAT' the Computer

Harness Adaptive Tester.

4. Provide specific information for the use of CHAT to perform voltage

and continuity testing for all wires and circuits interfacing the ECM.

This manual has been prepared for:

1. Professional Technicians in the field of automotive repair.

2. Students of Automotive Technology.

3. Automotive Enthusiasts who wish to know more about

contemporary automotive engine electronics.

This manual has been prepared with a "systems" approach:

1. Diagnosis and repair must be performed in a step by step method, to ensure

that you "isolate" the problem, and not simply replace what seems to be wrong.

2. Automotive systems are broken down so that you can see how they are intended

to work in a conceptual method. When you understand the general concept you

will be able to apply your understanding to systems and components which differ

from those included in this manual.

This manual is not intended to replace applicable service manuals pertaining to the

service of any automobile. This manual is intended to complement service manuals

specifically prepared by the vehicle manufacturer.

In order to understand the complex na￾ture of today's automobile we must be

able to speak and understand the lan￾guage used to describe these vehicles.

You may be reluctant to want to learn

anything, but you have made it this far by

purchasing this book. A book which you

can use and learn new technology from.

A book written to help you each and

every day on the job.

Actually, when you start to dig into this

material it will be fun and interesting.

The trick is to just take your time and

master these basic terms and concepts.

One thing that you really need to do is

understand how these things work, at

least on a simple level. This book will

approach everything on a simple level

and use this basic principle of under￾standing to build upon.

Some of the things which we will look at

in the beginning will seem too simple to

really work with. However, I have seen

too many repairs done incorrectly. When

you really analyze what you are doing the

bottom line really must be to get the car

fixed. Hopefully, this will happen the

first time or else you will have a recheck

to perform. Rechecks mean that you will

not be making money on the next car

waiting for you. Therefore, the fewer

rechecks the more money you ought to

make. That seems simple enough,

doesn't it?

Always try and do the job right the first

time even if it takes a few extra minutes.

One good example would be a water

pump. If it leaks then you will probably

have to do the whole job over and I don't

know of anyone who wants to redo a

water pump. The same sort of thinking

applies to this new technology. If the car

still has a driveability problem then it is

going to be a comeback and rechecks eat

your earnings.

NO RECHECKS

This book has been prepared with the

objective of presenting basic concepts

which apply to the modern automobile

which uses a small computer or ECM to

control fuel delivery to the engine. In

order to understand how this system

functions, you will be presented the basic

concepts relating to how air and fuel

management is accomplished.

If you know and understand the relation￾ships between the sensor inputs and

computer outputs you will be able to

diagnose problems which occur with the

modern automobile. No one book can

be expected to provide all information

which can apply to all situations. How￾ever, the information provided will be of

value when you must diagnose and re￾pair these vehicles.

As you gain experience with computer

equipped cars and trucks you will find

that they do perform and react in a

predictable way. There are certain

things which you must know and under￾stand. Some things must work or the

vehicle simply will not run. These facts

will be covered so that you will be able to

quickly and accurately determine if

these necessary inputs are present. Use

of a definite strategy will mean that your

diagnosis is done quickly and in a logical

procedure.

Your use of a definite method of analysis

will increase your productivity and reduce

the number of comebacks and your

number of rechecks. This increase in

productivity will make you a better tech￾nician which should also correspond to an

increase in your paycheck.

In order that you understand how this

system works we will first investigate the

ignition system. Understanding of

today's ignition systems is 100% essential.

Proper fuel delivery to the engine is based

upon this input signal and without it the

vehicle will not run due to loss of both

spark and fuel delivery.

NO WRENCHES ON

THE RED TERMINAL

Always remove the ground cable first. If you

accidentally hit some sheet metal you will not

risk blowing up the battery.

I believe that many technicians do not

have a good understanding of how igni￾tion systems operate. Therefore, we will

study a conventional point-type ignition

first. If you know and understand how

this system works you will not have any

difficulty with electronic systems. More

cars are being designed each year without

distributors. As you progress through

your study of this book, you will clearly

come to understand why a distributor is

not needed. As you learn how these

systems operate and how other inputs

can provide the same necessary signal

you will be able to figure out and trou￾bleshoot systems which you have not per￾sonally worked on yet.

As you study this manual and compare its

information to the cars which you work

with daily you will become a better tech￾nician. Additional education at your

local technical school or community col￾lege will also help you to be more profes￾sional in your duties. If you are not

already certified by ASE, you are encour￾aged to participate. ASE certification is

a highly desirable goal and those techni￾cians who wear the ASE patch take pride

in their accomplishment. You make your

living as a technician. Vehicles which you

work on daily are highly complex and the

more you know about these vehicles the

better off you are. Your need for techni￾cal literature and education have never

been greater. You demonstrate your

professionalism when you wear the ASE

certification patch.

YOUR TECHNICAL JOB

THE MORE YOU KNOW

THE MORE THINGS

YOU CAN FIX

FASTER &

MORE RELIABLE

EVERYONE BENEFITS

FROM TECHNICIAN

CERTIFICATION

SUPPORT IT!

I walked into my local Chevrolet dealer

and asked for a job as a junior mechanic

and grease monkey during my summer

break from college in 1969. That did not

last long; soon I was tearing apart engines

and trying to figure out how to get them

running again. The more things which I

could fix, the more work I got in the shop.

I drove my first race car in 1965. It was

while I was a senior in high school in State

College, Pennsylvania. We even raced in

the winter. I remember trying to run over

a snowbank during one event while rac￾ing on the icy surface. This interest in

racing has probably been the key to why

I have always kept a strong interest in

automotives.

Over the years I have raced many differ￾ent types ofvehicles including the likes of

jeep, ferrari, pantera, vega, corvair, mus￾tang, police cars, and my favorite, the

corvette. Those police cars came from

when I taught High Performance Driving

to police officers at the Texas Transpor￾tation Institute.

I have always felt that if you are going to

win on the track then you must field the

best car. Even if you happen to be the

best driver around, if your machine is not

set up properly then you cannot win. I

have never gone to an event with the idea

to lose. Of course I don't always win and

I do get beat sometimes, but I don't lose.

It really is a state of mind where you feel

confident about your ability and your

equipment. When you know what you

are supposed to do, and you do it well,

then you can really enjoy what and how

you do things. I would hope that you

personally feel that way about your

occupation ... if you do not then I hope

that this book will help you to gain this

type of confidence.

For a period of three years I was in the

position of resident engine instructor, at

one of the 31 GM training centers in

operation at that time, after having been

recruited by General Motors in 1983 . In

Detroit we would be given product infor￾mation which would be used to conduct

classes about new engine systems and

their operation for dealership techni￾cians who would attend our classes. All

this new information was great, but this

information had to be passed on to the

fellows and an occasional lady who actu￾ally "turns a wrench" to make a living. It

really was a lot of fun.

Additional qualifications to be your au￾thor to write this book besides my expe￾rience with GM, racing, and having been

a "Chevrolet Certified Technician"

would include formal college education

background of a BS, MA, and finally a

Ph.D. in industrial education from Texas

A&M University. In 1987 I was one of

375 people inducted into the Automo￾bile Hall of Fame in Midland, Michigan

as an "ASIA/ASE 'World Class' Techni￾cian" for holding all 16 ASE area certifi￾cations.

Way back in the old days, pre-computer

cars that is, we basically concerned our￾selves with three types of problems: 1)

fuel, 2) ignition, or 3) mechanical. How￾ever, today there is an additional 4) elec￾tronic problem area which really gives

technicians a tough time. This latest

addition to our problems is the most dif￾ficult to understand. You simply cannot

take apart a transistor with a 9/16" or

lOmm wrench. Since you cannot easily

disassemble this electronic stuff it means

that you will probably have to learn about

these things either on your own or in a

class somewhere. This book will help you

understand how automotive electronics

work and this book will help you fix

today's electronically complex cars.

When cars were simple it was not too

difficult to figure out which area theprob￾lem was in and then it could be attacked.

If there was a question about ignition,

then did spark come out of the plug wire?

If not then points were pretty easy to fix.

I remember a 1970 LT-1 corvette at the

dealership, the ticket said "won't run". I

found the car, it would crank but not start.

I popped off a plug wire and hung it on top

of the air cleaner wingnut; crank engine

again and no spark but the 12 volt test

light says power to the coil and a good

ground. Hmmm ... the points must be

locked up. Off with the chrome shroud,

remember this is a corvette, off with the

distributor cap ... what the .... So much for

my first introduction to transistorized

ignition.

Today's cars may affect you the same

way. There is no denying that cars are

much more complex than ever before

and there is no alternative to under￾standing how they operate. Because of

Federal regulations for improved fuel

and emission characteristics of our ve￾hicles it became necessary to develop

more sophisticated engine control sys￾tems to meet these new standards. Many

of you reading this book look favorably

on the past but you know that "simple"

cars are no longer built; also you know

that the carburetor is in fact only a "cali￾brated leak" which will not do the job

today.

Microprocessors are the heart of the

computer or Electronic Control Mod￾ule, ECM for short. Microprocessors get

information from many sensors placed

all over the vehicle. Microprocessors

take this information and run it through

the operational program recorded per￾manently inside the machine found on

10

ROMS and PROMS. After all this analy￾sis is done then some sort of output will

come from the ECM such as when to

inject fuel and how long the injectors are

to be held open.

This entire information transmission

process at first seems almost impossible

to figure out. However, this is not the

case. There are some very logical rela￾tionships which do exist and you as a

professional technician already know the

basic principles of engine operation. We

will take these things which you are al￾ready familiar with and use them as the

basis for all the new systems. New sys￾tems may be new but they accomplish the

same sort of things as the old systems.

Whether or not new systems are better is

something which most mechanics and

technicians have personal opinions

about ...j ust ask one! Let's face it, there is

no alternative ...y ou have to know how the

new systems operate if we are going to be

successful in this occupation.

How did you learn to be a technician in

the first place? Were you taught by other

mechanics or did you attend a technical

training program? I expect that you actu￾ally have some of both. You have already

invested heavily in your education; some

people would call this the "School of

Hard Knocks." You have invested thou￾sands of dollars in your tool box. Every

time the tool truck comes by you can

think of additional tools which will make

you more productive. Tools are an in￾vestment in your future, there is no other

alternative there.

When you finish reading this book you

will find it to be an excellent reference.

Others will want to use this book. As with

any tool you will need to have it available

at times. You know who borrows your

tools and this book is no exception. A

saying that I have seen on one master

technician's toolbox is "I would rather

loan you my dog than my tools. The dog

always comes home." It applies to this

book too.

IF YOU WANT TO FIRE TWO

SPARK PLUGS AT THE SAME

TIME, HERE IS HOW IT'S DONE.