Hatch S.N. Computerized engine controls

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Acknowledgments

I am very honored to be able to present a

textbook of such magnitude as this. But there are

those around me that I depend on greatly and

without whom this textbook would not be the suc-

cess it is today.

Many thanks to my family, my friends, and

my colleagues who have so encouraged me.

And many thanks to my students who, while they

were in my classes over the years, asked the

right questions that encouraged me to “find the

answer.”

I would like to thank the following people for

their efforts on the behalf of this textbook:

• My colleague, Kevin Dowell, who took the

time out of his busy schedule to offer me

technical advice in his area of expertise (and

also took the time to gather some waveforms

for me).

• My colleague, Larry Wilkinson, who volun-

tarily provided some research materials to

me.

• My brother, Terrence J. Hatch, who volun-

tarily spent some time to help me research a

couple of the topics that I updated.

• William K. Bencini, who allowed me to use

several of his photos in the Honda i-VTEC

portion of Chapter 17.

I would also like to thank my wife, Geralyn,

for her continued patience with the many hours

that this effort has required of me.

And finally, many thanks to the following for

their critical reviews and/or answers to questions

concerning this text:

Kevin Uhler

Southeast Community College

Milford, NE

Michael Malczewski

College of DuPage

Glen Ellyn, IL

David Christen

University of Northwestern Ohio

Lima, OH

Ken Mays

Central Oregon Community College

Bend, OR

William Roche

Danville Community College

Danville, VA

Lance David

College of Lake County

Grayslake, IL

The publisher would like to thank the author,

Steve V. Hatch, for providing the photographs

used throughout this edition of the textbook.

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605

Now that you have read this book, you might

be wondering how best to apply the information

when a vehicle is brought into your service bay

for diagnosis and repair. Sometimes it can be

difficult to put theory into action. This appendix

is designed to help the reader understand how

to convert the information contained in this book

into hands-on diagnostics.

NARROWING DOWN THE AREA

OF THE PROBLEM

If someone asked you to guess a number

between 0 and 1000 in a minimal number of

guesses, but with the promise that he/she would

also inform you as to whether each guess was

too high or too low, you would do well to begin

guessing with the number 500. This cuts the pos-

sibilities in half. And if their next response was

that your number was too high, your next best

guess would be 250, cutting the possibilities in

half again. So it is with diagnosing complex auto-

motive electronic systems.

Your initial goal in diagnosing a fault of any

type (hard fault or soft fault) should be to nar-

row down the problem area associated with the

symptom to as small an area as possible. You

may take several approaches to accomplish this.

Failure to reduce the possibilities can result in ex-

treme frustration, as most technicians have expe-

rienced at one time or another.

Use the following tips to help you narrow

down the area of the problem before you begin

pinpoint testing. You can thereby minimize your

frustration and increase your diagnostic effective-

ness in spite of the complexity of modern auto-

motive systems.

Talking to the Customer

First, when the vehicle is brought into your

shop, gather information from the customer and

record it on the repair order. Include as much in-

formation as possible about the conditions under

which the symptom appears. It is also important

to find out if the vehicle has been taken to a shop

for the same symptom prior to this service. If you

listen carefully, what the customer states about

the problem may provide clues to the type of

problem the vehicle has, such as “This problem

has been happening ever since. . . . That “ever

since” might be just the clue you need.

You might also ask the customer to show you

the problem as he/she is experiencing it. For ex-

ample, this author once received a repair order

identifying the symptom as “headlights will not

stay turned on” on a vehicle that had been pur-

chased new three days earlier. When I was un-

able to verify the symptom, I asked the customer,

who was in the waiting room, to come back to

my service bay and show me the problem she

was experiencing. She literally reached through

the open driver’s door window, pulled back on the

Appendix A

Approach to Diagnostics

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606 Appendix A Approach to Diagnostics

“flash-to-pass” switch, and said, “See, when I let

go, the headlights turn off.” I then explained to her

that, though this new vehicle was new technol-

ogy in her eyes, it still had a traditional push/pull

headlight switch in the dash.

Unfortunately, in many shops, the technician

is not encouraged to speak directly with the cus-

tomer except as a last resort.

Symptom Verification

The first real step in diagnosis is to attempt

to verify the exact symptom. If the symptom can

be verified, you are likely dealing with a hard

fault. If the symptom cannot be verified, you are

likely dealing with a soft fault. Hard faults should

always be diagnosed before attempting to diag-

nose any soft faults. While there are some differ-

ences between diagnosing a hard fault and a soft

fault, most of the following information applies to

diagnosing faults of either type.

With your understanding of how the system

is designed to operate, symptom verification can

help you narrow down the area in which you need

to perform pinpoint tests. In fact, what you are re-

ally doing is mentally creating a flowchart. For ex-

ample, if the customer complains that there seems

to be a short in the exterior lighting circuits be-

cause other circuits seem to energize the running

lights (park, tail, and side marker lights), the first

step would be to gain an understanding of how the

system is designed to operate. If it is an unfamil-

iar system, this can be done through the electri-

cal schematics associated with the system. (Ever

notice how most flowcharts also include electrical

schematics?) The next step would be to verify the

exact symptom. This can be accomplished by op-

erating each of the exterior lighting systems and

noting the results. For example, if the exterior run-

ning lights illuminate when the left directional sig-

nal is activated but not with the right directional,

it is likely that the short is located on the left side

of the vehicle. If the exterior running lights illumi-

nate when the brake pedal is depressed, the short

is at the rear of the vehicle. Thus, verification of

the exact symptom can be used to narrow down

the problem area, in this case to the left rear cor-

ner of the vehicle. Next perform a visual check

at that corner of the vehicle, beginning with the

bulbs—you may find a dual-filament bulb that has

a filament that has broken loose and is physically

touching the other filament. Because you nar-

rowed the problem down to one corner of the ve-

hicle by using the exact verified symptoms, you

do not have to perform visual checks and pinpoint

tests at all four corners of the vehicle—only at the

one corner identified by the symptoms. This type

of approach ultimately results in less frustration in

that it is easier to perform pin-point tests of a par-

ticular area as opposed to tearing apart harnesses

and components throughout the entire vehicle.

Visual Inspection

A thorough visual inspection of the system(s)

associated with the symptom should be per-

formed. If this is done properly and conscien-

tiously, problems can often be identified at this

time. Additional visual inspections may need to

be performed as the area of the fault is further

narrowed down through diagnostic processes

such as code pulling and gas analysis.

Assistance from the Onboard Computers

An important aid to help the technician nar-

row down the problem area is to take advantage

of the abilities of onboard computers; they are

programmed to offer you their assistance.

Diagnostic Trouble Codes. Modern on-

board computers are programmed, at the very

least, to allow the technician to pull memory

diagnostic trouble codes (DTCs). Others will

allow the technician to perform a self-test of the

system. Both memory codes and self-test codes

can quickly identify a problem area or circuit for the

technician. But if a DTC is set as the result of an

electrical open in a specific circuit, the technician

must still perform pinpoint tests to identify the

exact location and cause of the open.

Data Stream. All OBD II systems and most

pre–OBD II systems allow the technician to look

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at data stream PIDs and related information con-

cerning sensor values and actuator commands.

This is extremely effective in helping the technician

to narrow down the problem to a specific area

or circuit. But suppose, for example, the data

stream information identifies an NTC thermistor

circuit as reporting a temperature of ⫺40°F; while

the technician now knows that there is an open

in the specific circuit, further pinpoint tests must

be performed to identify the exact location and

cause of the open.

Other Scan Tool Functions. Most com-

puters will also perform other functional tests,

either using manual methods to trigger these

functions or with the help of a scan tool. For

example, the technician may be able to use a

scan tool to command the computer to energize

a specific actuator (active command or bi-

directional control). This helps the technician to

quickly narrow down a problem associated with

that system to either the input side or the output

side of the computer. If an actuator that does

not operate normally now operates under the

scan tool’s direction, we know that the computer

can successfully energize the actuator, thus

eliminating the output side of the computer as

a possible fault; the technician would check the

sensors, switches, and other inputs next. But

if the actuator will not operate when the scan

tool commands it to, the actuator and its related

wiring/connectors should be checked.

Other functional tests may also be available,

depending upon the scan tool and the vehicle

itself. For example, on some systems a scan

tool can command the PCM to conduct a cylin-

der power balance test (this may be built into the

PCM’s program or the scan tool’s program).

PCM’s versus Other Control Modules.

These scan tool diagnostic features are not

limited to engine control systems; they also

apply to other electronic systems on today’s

vehicles. For example, a scan tool may also be

used to pull memory codes, initiate a self-test,

or look at data stream information on many

antilock brake systems, body control systems,

instrument clusters, and so on. Certain non-

engine systems, particularly on older vehicles,

may allow the technician to manually trigger

memory code pulling or self-tests, such as a

test of the Electronic Automatic Temperature

Control (EATC) system, by pushing various

combinations of buttons on the climate control

head. If the computer is programmed to help

you, take advantage of it.

Also, many modern scan tools offer a mode

that checks all onboard computers for any fault

codes with a single scan tool request, thus allow-

ing the technician to determine very easily any

fault codes associated with any computer on the

vehicle without having to select each computer

individually in the scan tool’s menu.

Exhaust Gas Analyzer

A third approach to narrowing down the prob-

lem area when diagnosing an engine system for

poor performance, poor fuel mileage, or failed emis-

sion tests is to use an exhaust gas analyzer to cap-

ture exhaust readings at both idle and 2500 RPM,

and then to use these readings to give you an idea

of the type of problem that you are attempting to

diagnose. For example, a high CO reading would

indicate that you should look for problems that could

result in a rich air/fuel ratio—either too little air or

too much fuel. As a result, analyzing the exhaust

gasses of an engine can help a technician quickly

narrow down the problem area, although it cannot

identify the exact problem. An exhaust gas analyzer

becomes an invaluable tool when attempting to

minimize the frustration factor.

When using an exhaust gas analyzer as

a diagnostic tool, use the gasses to determine

the actual air/fuel ratio and Lambda values (see

Chapter 16 for an explanation of Lambda). Newer

exhaust gas analyzers perform this calculation for

you from the measured gasses. If you are using

an older analyzer that does not perform this task,

use an automated “air/fuel ratio and Lambda”

calculator that is available on the Internet such

as the one found at the International Automotive

Technicians’ Network (IATN) (http://www.iatn .net).

Simply enter your four or five measured gasses

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608 Appendix A Approach to Diagnostics

(with or without the NO

value) in the automated

calculator to calculate the air/fuel ratio and

Lambda values. It is very helpful to know what

these values are when attempting to narrow

down the problem area. This will also serve as an

early indicator as to whether or not the PCM is in

proper control of the air/fuel ratio.

Verifying PCM Control of the Air/Fuel Ratio

When diagnosing a complaint of poor engine

performance, poor fuel economy, or an emissions

test failure, you will need to verify the ability of

the PCM to properly control the air/fuel ratio. This

can be done through the primary oxygen sensor’s

voltage waveform, but only if the oxygen sensor

itself has first been tested and proved to be in

good condition.

Testing the Oxygen Sensor. To verify the

oxygen sensor, use a DSO to monitor the oxygen

sensor’s waveform while forcing the air/fuel ratio

both rich and lean. This can be done on most

vehicles by simply throttling the engine in the

service bay. On a fuel-injected engine, suddenly

opening the throttle (acceleration) results in a rich

air/fuel mixture, and allowing the throttle to close

(deceleration) results in a lean air/fuel mixture. If

needed, a propane enrichment tool can be used

to force the mixture rich. Then suddenly turning

off the propane will force the mixture lean.

A zirconia-type oxygen sensor should be ca-

pable of exceeding 800 mV while the air/fuel ratio

is rich, then descending to less than 175 mV when

the air/fuel ratio is lean. It should be able to switch

between 300 mV and 600 mV in either direction in

less than 100 ms. It should never show a negative

value. Any failure in any of these areas is cause

for replacement. If you replace the oxygen sensor,

drive the vehicle about 10 miles to break in the

new oxygen sensor before you attempt to test it.

Testing the PCM’s Ability to Control the

Air/Fuel Ratio. Once the oxygen sensor has

been verified, sample the oxygen sensor waveform

with a DSO while driving the vehicle on a road

test. Be sure to have another technician drive the

vehicle so that you can safely monitor the DSO.

(A scan tool with a data-graphing capability may

also be used.) The oxygen sensor should show

a consistent cross-counting of its voltage to both

sides of the stoichiometric value. Additionally, fuel

trim values should be monitored with a scan tool

during the road test. The short-term fuel trim should

be reacting to the oxygen sensor’s voltage. If the

vehicle has electronic fuel injection (either TBI or

PFI), the oxygen sensor’s voltage should indicate

a lean condition during vehicle deceleration. All of

this indicates that the PCM is in proper control of

the air/fuel ratio. If the oxygen sensor’s voltage

indicates that the air/fuel ratio is pegged either

rich or lean, or is averaging outside of the 400- to

500-mV range (zirconia-type O

sensor), the PCM

is not in proper control of the air/fuel ratio and the

following steps should be taken to narrow down

the area of the problem to the electronics or to

something mechanical.

Narrowing Down the Problem Area to an

Electronic Fault or a Mechanical Fault. If the

oxygen sensor’s voltage is pegged either rich or

lean, compare this signal with the pulse-width

command to the fuel injectors. If the oxygen

sensor’s voltage is pegged lean and the pulse-

width command indicates that the PCM is

attempting to enrich the air/fuel ratio, we can

rule out the electronics (sensors and computer)

as being responsible for the fault—the problem

is mechanical and is outside of the computer’s

ability to control it. Likewise, if the oxygen sensor

voltage is pegged rich and the pulse-width

command indicates that the PCM is attempting

to lean out the air/fuel ratio, we can again rule

out the electronics as being responsible for the

fault—again, the problem is mechanical. When

the fault is identified as mechanical, look for the

following types of problems:

• vacuum leaks

• plugged or leaking fuel injectors

• plugged fuel filter

• ruptured fuel pressure regulator diaphragm

(return-type system)

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Appendix A Approach to Diagnostics 609

• false air upstream of the oxygen sensor from

either an exhaust leak or a faulty secondary

air-injection system

If the pulse-width command to the fuel injec-

tors indicates that the PCM is not reacting prop-

erly to the oxygen sensor signal (and is in fact

responsible for the pegged rich or lean condi-

tion), then the problem is electronic. When the

fault is identified as electronic, test the following

areas:

• sensors and other input circuits

• 5-V reference voltage to the sensor (TPS, for

example)—indicative of the voltage that is

also applied to the computer’s internal logic

gates

• excessive resistance in the PCM’s power or

ground circuits (voltage drop should not ex-

ceed 100 mV total in either the power side or

in the ground side)

• If all above tests are okay, replace the PCM

itself.

Using a scan tool to look at fuel trim values

in comparison to the oxygen sensor value is also

an excellent tool for determining if the fault is

electronic or mechanical. However, when using

fuel trim values, verify that the PCM is operating

in the correct fuel trim cell for the current operating

condition. If an engine load sensor (MAP or MAF

sensor) is reporting that the engine is under more

load than it really is, the PCM will use an incorrect

fuel trim cell in an upper load area; as a result,

the PCM will be locked into a window of longer

fuel injector pulse widths. If you simply note the

fuel trim values without noting the fuel trim cell

number, these values will indicate that the PCM

is attempting to subtract fuel—and yet the total

pulse width will be too long for the condition. If in

doubt, back up your fuel trim values by reading

actual PCM-commanded injector on-time, either

with a scan tool or with a DSO/DVOM. A helpful

tool in this area is a scan tool that shows the

values of all fuel trim cells, such as the PC-

based scan tool from Automotive Test Solutions

(http://www.automotivetestsolutions.com).

PINPOINT TESTING

To isolate any remaining hard faults, visual-

ize the electrical circuit in three parts: the source

(battery or alternator), the circuitry, and the load

component. The source is the first component

that should be verified. For example, if the starter

cranks slowly, check the battery’s open-circuit volt-

age and then load test it. It is a good idea to test

the battery’s open-circuit voltage for symptoms

associated with smaller load components, even

if the starter cranks normally, due to the effects

of low open-circuit voltage on computer opera-

tion. Also, do not overlook the effects of excessive

alternator ripple on computer-controlled systems.

To test this, connect a DVOM between the alterna-

tor positive and negative terminals while scaled to

an AC voltage scale. With the engine running, AC

voltage should stay well below 500 mV, preferably

less than 300 mV. Excessive alternator ripple can,

of course, also be seen with a DSO (lab scope).

To test the circuitry, use a DVOM on a DC

voltage scale to perform voltage-drop tests on

both the positive and negative sides of the circuit

(see the section about voltage-drop testing

in Chapter 6). This verifies the integrity of the

circuitry used to connect the source to the load

component. While 100 mV per connection is

allowed in normal circuits (and even 200 mV

per connection in starter circuits due to the high-

current, low-resistance designs of these circuits),

a power or ground circuit that is used to power up

a PCM (or other computer) should never exceed

100 mV total voltage drop in either the positive

circuit or in the negative circuit with the key on,

engine off (KOEO). This tight specification is due

to the high-resistance, low-current flow designs

of these circuits. Many good PCMs are replaced

simply because of a poor power or ground circuit.

Therefore, after verifying each of the input and

output circuits, but before replacing the PCM,

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you should get in the habit of using an electrical

schematic to identify each of the PCM’s power

and ground terminals. Then with the ignition on,

perform voltage-drop tests between the battery

and the PCM.

Ultimately, the load component can be tested

by the following methods. If the load component

is an electronic control module, simple elimina-

tion of possible faults elsewhere in the circuitry

through voltage-drop testing is used most often

to narrow down the problem to the control module

itself. Other load components can be tested elec-

trically and functionally. Electrical tests involve

the use of an ohmmeter to measure a solenoid’s

(or relay’s) resistance in the windings, or jumper

wires to energize the component. Functional test-

ing can be done using other methods, depending

upon the type of actuator being tested. For ex-

ample, use a vacuum pump opposite a vacuum

gauge to test a vacuum solenoid.

Other tools that can make pinpoint testing

easier include DSOs, logic probes, and breakout

boxes (see Chapter 6). DSOs can show voltage

waveforms, logic probes can quickly check for

the presence of ignition primary, and fuel injector

signals and breakout boxes can be used to im-

prove computer circuit accessibility without back-

probing.

Finally, flowcharts and electrical schematics

are invaluable when it comes to pinpoint testing.

A flowchart is written according to the design en-

gineer’s understanding of system operation. An

electrical schematic helps you as a technician to

understand system operation.

Technical Service Bulletins

The next step that should be performed is

checking the manufacturer-issued Technical Ser-

vice Bulletins (TSBs). These are usually available

either through electronic information systems

or directly from the manufacturer. A TSB is a

manufacturer-suggested repair for a problem the

manufacturer is already aware of. It may involve

a simple fix or it may involve something as in-

depth as replacing a PCM or a PROM chip in the

PCM, or even reflashing of the PCM. Make sure

that you use the latest TSB issued for the particu-

lar symptom that you are trying to diagnose and

repair, as multiple TSBs have sometimes been

issued in attempting to correct a single problem.

Ultimately, access to TSBs is critical to a techni-

cian attempting to diagnose engine performance

problems and can lead to increased diagnostic

effectiveness.

Do Not Overlook the Basics

When warranted, the basic engine systems—

compression, ignition, and air/fuel delivery—must

not be forgotten. A vacuum gauge can be used

to quickly give the technician ideas about pos-

sible fault areas that should be tested further. A

cylinder power balance test (performed either

with an ignition scope, through a functional test

programmed into the PCM [as on Ford EEC-IV

systems], or with a scan tool [many modern scan

tools]) can quickly identify cylinders that may be

lacking compression, spark, or fuel delivery. If one

or more cylinders are identified as being weak,

the following areas should be looked at.

Compression. Performing a compression

test on each of the cylinders while the starter is

cranking the engine and the throttle is held open

(known as a cranking compression test ) tests for

cylinder seal. For example, a burned valve could

easily cause a particular cylinder to fail this test

due to the leak it creates.

However, if all cylinders pass this test and

spark and fuel are verified with an exhaust gas

analyzer, a running compression test should be

performed. To perform this test, all spark plugs

must be reinstalled except the one in which the

compression gauge is connected. Then the engine

is started. Once the engine is running, momen-

tarily release the compression gauge pressure.

Now note the compression pressure at idle, at

1500 RPM, and on a snap throttle. At idle and

1500 RPM, the pressure reading will be about

one-half of the cranking compression due to

the closed throttle and the faster piston speed.

Because of the faster piston speed, this is a very

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Appendix A Approach to Diagnostics 611

poor test to check cylinder seal, but it is an excel-

lent test to check and compare each cylinder’s

volumetric efficiency (the cylinder’s ability to

breathe in and out). It is difficult to apply a hard

specification to this test because of different cam-

shaft grinds; instead, the cylinders should simply

be compared. One or two cylinders showing lower

readings than the rest indicates an inability to

breathe in because of an improper opening of the

intake valve, and one or two cylinders showing

higher readings than the rest indicates an inability

to breathe out because of an improper opening

of the exhaust valve. This inability of the engine

to breathe properly is caused by problems in the

valve train such as loose rocker arms, worn push

rods/lifters, or a worn cam lobe. Because these

valves still seal when closed, the cranking com-

pression test does not identify the problem. One

point to note: Have some spare Schrader valves

on hand for your compression gauge when per-

forming running compression tests.

Ignition. If the engine cranks but does not

start, both secondary ignition and primary ignition

should be checked. If the tach reference signal

is not present, either from a distributor or from a

crankshaft sensor, neither secondary spark nor

fuel injection pulses will be present. If there is a

spark being produced in an ignition coil or if the

fuel injectors are being pulsed, the distributor

pick-up/crankshaft sensor is functioning.

If the engine starts and runs but has perfor-

mance problems or misfire present, the second-

ary ignition waveform should be checked on an

ignition oscilloscope. And if a shorted primary coil

winding is a possibility, use a DSO coupled with

a current probe to test each primary coil winding

through its current waveform.

Air/Fuel. This area includes the common

maintenance items such as air and fuel filters and

the PCV valve and crankcase ventilation filter.

Also, if the engine has failed a cylinder power

balance test, measure the exhaust emissions

with an exhaust gas analyzer at both idle and

1500 RPM. Then turn off the engine and disable

the spark for the failed cylinder. On distributor and

waste spark systems, simply use a jumper wire

to short one spark plug wire to or from engine

ground. On coil-on-plug (COP) systems, simply

disconnect the primary connector from the coil

for the failed cylinder. Now restart the engine. If

burned hydrocarbons increase dramatically from

their previous values, the failed cylinder has both

spark and (at least some) fuel present. If this is

the case, then cranking and running compression

tests should be performed (if they have not

already been performed).

Another concern is the quality of the fuel. If

excessive alcohol in the fuel is a possibility, mix

a sample of the vehicle’s fuel with some water

in a graduated cylinder. The gasoline will float

above the water, creating a gasoline/water line

between them. Shake the cylinder vigorously for

30 seconds and then let it settle. After settling, if

the height of the gasoline/water line is increased,

it is because of alcohol content in the gasoline

sample—the alcohol separates from the gaso-

line and combines with the water during this test.

Use the increase in the height of the gasoline/

water line to calculate the percentage of alcohol

content. Except for E85 fuel (when working on

an E85-capable vehicle), any alcohol content in

excess of 10 percent can create fuel volatility

problems.

Finally, a fuel test kit can be used to measure

the specific gravity of a sample of the vehicle’s

gasoline (similar to specific gravity tests of a lead

acid battery’s electrolyte when the cell caps were

removable). Although it does not directly measure

the fuel’s Reid Vapor Pressure (RVP), the fuel’s

specific gravity will be indicative of the fuel’s vola-

tility. (RVP measures a fuel’s volatility by measur-

ing how much pressure the fuel will create in a

confined space when heated to 100°F, at which

pressure the fuel quits boiling/vaporizing.) The

specific gravity of the fuel should also quickly alert

you to any diesel fuel that might have been put

into a gasoline engine’s fuel tank inadvertently.

Flowcharts

Flowcharts are designed to aid the techni-

cian in making appropriate pinpoint tests that are

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