Hatch S.N. Computerized engine controls

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612 Appendix A Approach to Diagnostics

applicable to the DTC or symptom. When using

them, be sure to perform the following:

• Read and follow the test instructions care-

fully.

• Do not skip any test steps and assume their

outcome—this can result in misdiagnosis

and/or wasted time.

• Be sure of your equipment—does your DVOM

or DSO read battery voltage when the leads

are placed across the battery? Or does your

jumper wire have continuity?

• Make the repair as indicated in the final

step—you can be confident of what it is ask-

ing you to do if you have carefully followed all

test steps and not skipped any.

Reducing Your Dependence

on Flowcharts

While they are a necessary diagnostic tool,

flowcharts may be restrictive for the following

reasons:

• Their content is limited to the engineer’s abil-

ity to imagine all potential problems that could

develop with the system.

• They will occasionally contain an error.

• They are time consuming—it can take you

longer to read and understand what the flow-

chart is asking you to test than the flat rate for

the job pays.

• If someone has altered the OEM design in

the aftermarket, the flowchart may no longer

apply.

Another approach that will reduce your

dependence on flowcharts is to diagnose the

system through your own understanding of how

the system is designed to operate. The following

is required for a technician to understand the

operation of an unfamiliar system:

• a working knowledge of electrical laws

• a working knowledge of electronics—inputs,

processing, and outputs

• the ability to read and interpret an electrical

schematic

Interpreting an Electrical Schematic. Fol-

lowing are a few ideas that will help you interpret

a complex electrical schematic. It helps to begin

by copying or printing out the electrical schematic

so that you can draw on it.

• First: Identify the components. Highlight the

components with a yellow highlighter if nec-

essary. This quickly simplifies a seemingly

complex schematic. It also keeps you from

inadvertently attempting to interpret the out-

line of a module as a circuit.

• Second: Identify the powers and grounds.

You might use red or orange for power and

green for grounds.

• Third: Identify the input and output circuits.

You might use blue for inputs and purple for

outputs. Bear in mind that sometimes an

ignition-switched voltage operates as an in-

put to a control module, as with an illuminated

entry system. In this system, battery voltage

is used to power up the module. The ignition

voltage only acts as an input to let the module

know that it may turn off the interior lights.

• Fourth: Identify any data busses used for

communication between computers.

Other Diagnostic Resources

In most difficult diagnostic situations, the

odds are that someone else, somewhere else,

has already encountered and solved the problem

that you are striving to solve. Following are some

examples of these resources.

International Automotive Technicians’ Net-

work. The International Automotive Tech nicians’

Network (IATN) can be a valuable resource in

helping the technician solve difficult problems.

Accessible at http://www.iatn.net, this Web site

offers many valuable tools, from technician

interaction to manufacturer-provided information

and other technical resources. IATN offers both a

free membership and a sponsoring membership.

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Appendix A Approach to Diagnostics 613

Identifix. An updated version of IATN,

Identifix offers an online diagnostic information

service designed to aid the automotive service

technician in diagnosing difficult problems.

Accessible at http://www.identifix.com, this Web

site is administered by Automotive Information

Systems (AIS), Inc. (founded in 1987). They

employ 30-plus factory-certified ASE master

technicians. Unlike IATN, Identifix technicians

work to verify information from other technicians

before posting it to their Web site.

World Wide Web. Finally, the World Wide

Web (www) can sometimes be helpful in solving

a difficult problem. Simply perform a “Google”

search for a specific symptom on a specific make,

model, and year of vehicle and you may find a

helpful repair hint.

ADDITIONAL INFORMATION

CONCERNING SOFT FAULT

DIAGNOSIS

This question is often asked: How can I pin-

point test a fault when the symptom does not

appear to be present? There are several ans-

wers to this question. Certainly, past experience

on like models with similar problems counts for

something. Unfortunately, this approach often

results in improper repairs and unneces sary

parts replacement. A better approach is sug-

gested in the following paragraphs.

The first step is to determine whether the

PCM has stored any DTCs in memory that could

direct you to a probable problem area. At the very

least, a memory DTC can help you determine if

the reason for an “intermittent engine shutdown

until cooled” is the likely result of the ignition

system or the fuel system. However, additional

tests can be performed to pinpoint test the exact

cause, even when the symptom does not appear

to be present.

If the soft fault is in the circuitry, perform-

ing voltage-drop tests of the circuitry will locate

the fault, even when the circuit appears to be

functioning normally. Remember, voltage-drop

testing is used to identify excessive unwanted

resistance in the circuitry. This excessive un-

wanted resistance increases with an increase in

temperature to the point of creating a symptom.

Likewise, this resistance decreases with a de-

crease in temperature, to the point that the cir-

cuit again becomes operational. The excessive

unwanted resistance does not totally disappear,

even when the circuit appears operational and

the symptom does not appear to be present.

Thus, if a soft fault is in the circuitry, voltage-

drop testing can identify the circuit problem even

without the symptom present. While the voltage-

drop reading will not be as excessive as when

the symptom is present, it will still likely be above

acceptable limits.

If the soft fault is in the load component,

using a DSO (lab scope) and a low-current probe

to sample the current waveform of the load com-

ponent can identify faults in the load component

that can cause intermittent operation (see Chap-

ter 6). This is particularly true of motors. The cur-

rent waveform can identify an open or shorted

winding within the motor as well as some other

faults that will weaken the motor’s strength and

result in intermittent symptoms associated with

the motor. In this way, a load component can be

proved to be defective, even though it may still

be operational while in your shop. This technol-

ogy allows you to show your customer a printed

waveform that proves that a load component is

not being replaced needlessly. It can even allow

you to identify a load component that is ready to

fail, even before symptoms have been encoun-

tered.

SUMMARY

This appendix is designed to help the reader

put some of the information contained in various

chapters of this book into perspective. No one

chapter is going to provide a quick repair guide

to all the problems encountered on today’s com-

plex vehicles. Rather, it takes an understanding

of the concepts covered in the first chapters, in

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614 Appendix A Approach to Diagnostics

combination with the product-specific information

covered in the later chapters, to effectively diag-

nose and repair today’s modern systems. Even

then, in spite of this author’s best efforts, none

of us will ever fully retain all of the system and

product-specific information necessary for effec-

tive repair and diagnosis. Therefore, a source of

product-specific information is as necessary as

any other tool that you might use in your busi-

ness. These service manuals may be paper or

electronic, but they are very necessary.

A good technician today cannot know it all.

Rather, he/she must strive to understand the op-

erating and diagnostic concepts associated with

today’s modern systems and then know where to

look up the product-specific information when an

unfamiliar system is encountered. If this textbook

has provided the reader with an understanding of

the underlying concepts and with the knowledge

required to comprehend the paper/electronic ser-

vice manual literature, then our goal has been

achieved.

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615

This appendix contains figures that provide

terminology and acronyms for common (non–

manufacturer-specific) terms, OBD II terms, and

terms for both domestic and Asian vehicles, as

well as many of their OBD II counterparts as

applicable. The figures list the manufacturers’

terms and acronyms in the same order that these

manufacturers are addressed through the chap-

ters of this book.

Appendix B

Terms and Acronyms

Term Acronym Term Acronym

Air Conditioning A/C Ohms

⍀

Alternating Current AC Oxides of Nitrogen NO

Amps A Oxygen O

Analog Volt/Ohm Meter AVOM Park/Neutral P/N

Carbon Dioxide CO

Ported Vacuum Switch PVS

Carbon Monoxide CO Positive Crankcase Ventilation PCV

Digital Volt Meter DVM Programmable Read-Only Memory PROM

Digital Volt Ohmmeter DVOM Pulse-Width Modulated PWM

Direct Current DC Random-Access Memory RAM

Hydrocarbons HC Read-Only Memory ROM

Ignition IGN Revolutions per Minute RPM

Instrument Panel IP or I/P Tachometer TACH

Key On, Engine Crank KOEC Thermal Vacuum Switch TVS

Key On, Engine Off KOEO Thermostatic Air Cleaner TAC

Key On, Engine Running KOER Variable Pulse Width VPW

Miles per Hour MPH Vehicle Identification Number VIN

Nitrogen N

Volts V

Normally Closed N/C Water H

Normally Open N/O Wide-Open Throttle WOT

Figure B–1 Common terms and acronyms.

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616 Appendix B Terms and Acronyms

OBD II Term OBD II Acronym

Air-Conditioning Clutch ACC

Air-Conditioning Cycling Switch ACCS

Air-Conditioning Demand ACD

Barometric Pressure sensor BARO sensor

Camshaft Position sensor CMP sensor

Canister Purge CANP

Crankshaft Position sensor CKP sensor

Data Link Connector DLC

Diagnostic Link Connector DLC

Diagnostic Trouble Code DTC

Distributor Ignition* DI

Early Fuel Evaporation EFE

Electronic Ignition** EI

Engine Coolant Temperature sensor ECT sensor

Evaporative Emission Control System EVAP

Flexible Fuel FF

Generator (Alternator) GEN

Heated Oxygen Sensor HO

Idle Air Control IAC

Idle Speed Control ISC

Intake Air Temperature sensor IAT sensor

Knock Sensor KS

Long-Term Fuel Trim LTFT

Malfunction Indicator Lamp MIL

Malfunction Indicator Light MIL

Manifold Absolute Pressure sensor MAP sensor

Mass Air Flow sensor MAF sensor

Mixture Control solenoid MC solenoid

Multiport Fuel Injection MFI

Oxidation Catalyst OC

Oxygen Sensor O

Power Steering Pressure PSP

Powertrain Control Module PCM

Pulsed Secondary Air Injection Reaction system PAIR system

Secondary Air Injection Reaction system AIR system

Sequential Fuel Injection SFI

Short-Term Fuel Trim STFT

Speed Density SD

Three-Way Catalyst TWC

Throttle Body Injection TBI

Throttle Position Sensor TP sensor or TPS

Torque Converter Clutch TCC

Transmission Control Module TCM

Vehicle Speed Sensor VSS

*Mechanical spark distribution using a single coil and a distributor.

**Electronic spark distribution using multiple coils and no distributor.

Figure B–2 OBD II standardized terms and acronyms.

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Appendix B Terms and Acronyms 617

GM Term GM Acronym OBD II Acronym

Air Injection Reaction AIR AIR

Assembly Line Communication Link ALCL DLC

Assembly Line Diagnostic Link ALDL DLC

Backpressure EGR BPEGR BPEGR

Barometric Pressure sensor BARO sensor BARO sensor

Block Learn LTFT

Charcoal Canister Purge CCP CANP

Check Engine Light CEL MIL

Climate Control Panel CCP

Computer Command Control CCC or C3

Computer-Controlled Coil Ignition C3I

Coolant Temperature Sensor CTS ECT sensor

Digital Fuel Injection DFI

Direct Ignition System DIS

Early Fuel Evaporation EFE EFE

Electronic Climate Control ECC

Electronic Climate Control Panel ECCP

Electronic Control Module ECM PCM

Electronic Fuel Injection EFI

Electronic Spark Control ESC

Electronic Spark Timing EST

Evaporative Emission Control System EECS EVAP

Exhaust Gas Recirculation EGR EGR

Fuel Data Panel FDP

Heated Oxygen Sensor HO

S HO

High Energy Ignition HEI

Idle Air Control IAC IAC

Idle Load Compensator ILC

Idle Speed Control ISC ISC

Integrated Direct Ignition IDI

Integrator STFT

Manifold Absolute Pressure sensor MAP sensor MAP sensor

Manifold Air Temperature sensor MAT sensor IAT sensor

Mass Air Flow sensor MAF sensor MAF sensor

Mixture Control solenoid M/C solenoid MC solenoid

Multiport Fuel Injection MFI MFI

Oxygen Sensor O

S O

Port Fuel Injection PFI MFI

Power Steering Switch PSSw PSP

Pulse Air Injection Reaction PAIR PAIR

Sequential Fuel Injection SFI SFI

Throttle Body Injection TBI TBI

Throttle Position Sensor TPS TP sensor or TPS

Torque Converter Clutch TCC TCC

Tuned Port Injection TPI

Vehicle Control Module VCM

Vehicle Speed Sensor VSS VSS

Figure B–3 General Motors terms and acronyms.

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618 Appendix B Terms and Acronyms

Ford Term Ford Acronym OBD II Acronym

Adaptive Strategy LTFT/STFT

Air Charge Temperature sensor ACT sensor IAT sensor

Air-Conditioning Clutch ACC

Air-Conditioning Cycling Switch ACCS

Air-Conditioning Demand ACD

Backpressure EGR BPEGR BPEGR

Barometric Pressure sensor BP sensor BARO sensor

Brake On/Off switch BOO switch

Canister Purge CANP CANP

Central Fuel Injection CFI TBI

Clutch Engaged Switch CES

Computer-Controlled Dwell CCD

Crankshaft Position sensor CP sensor CKP sensor

Cylinder Identification CID

Delta Pressure Feedback EGR sensor DPFE sensor

Differential Pressure Feedback EGR sensor DPFE sensor

Distributorless Ignition System DIS

Dual Plug Inhibit DPI

EGR Control solenoid EGRC solenoid

EGR Valve Position sensor EVP sensor

EGR Valve Regulator solenoid EVR solenoid

EGR Vent solenoid EGRV solenoid

Electronic Control Assembly ECA PCM

Electronic Distributorless Ignition System EDIS

Electronic Engine Control EEC I, II, III, IV, V

Electronic Fuel Injection EFI MFI

Engine Coolant Temperature sensor ECT sensor ECT sensor

Exhaust Gas Oxygen sensor EGO sensor O

Exhaust Gas Recirculation EGR EGR

Failure Mode Effects Management FMEM

Feedback Carburetor Actuator FBCA

Fuel Pump Monitor FPM

Heated Exhaust Gas Oxygen sensor HEGO sensor HO

Idle Speed Control ISC ISC

Idle Tracking Switch ITS

Ignition Diagnostic Monitor IDM

Inferred Mileage Sensor IMS

Inlet Air Solenoid IAS

Integrated Relay Control Module IRCM

Integrated Vehicle Speed Control IVSC

Keep-Alive Memory KAM

Keep-Alive Power KAPWR

Key On, Engine Off KOEO

Key On, Engine Running KOER

Knock Sensor KS KS

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Appendix B Terms and Acronyms 619

Ford Term Ford Acronym OBD II Acronym

Limited Operational Strategy LOS

Malfunction Indicator Lamp MIL MIL

Manifold Absolute Pressure sensor MAP sensor MAP sensor

Mass Air Flow sensor MAF sensor MAF sensor

Microprocessor Control Unit MCU

Neutral Drive Switch NDS

Neutral Gear Switch NGS

New Generation Star Tester NGS

Octane Adjust OCT ADJ

Power Steering Pressure Switch PSPS PSP

Pressure Feedback EGR sensor PFE sensor

Profile Ignition Pickup PIP

Programmable Speedometer/Odometer Module PSOM

Self-Test Automatic Readout tester STAR tester

Self-Test Connector DLC

Self-Test Input STI

Self-Test Output STO

Sequential Electronic Fuel Injection SEFI SFI

Service Bay Diagnostic System SBDS

Signal Return SIG RTN

Spark Angle Word SAW

Spark Output SPOUT

Speed Control Command Switches SCCS

Temperature Compensated Pump TCP

Thermactor Air Bypass TAB

Thermactor Air Diverter TAD

Thick Film Integrated TFI

Throttle Air Bypass TAB

Throttle Kicker TK

Throttle Position sensor TP sensor TP sensor or TPS

Vane Air Flow meter VAF meter

Vane Air Temperature sensor VAT sensor IAT

Variable Reluctance Sensor VRS

Variable Venturi VV

Variable Voltage Choke VVC

Vehicle Power VPWR

Voltage Reference VREF

Figure B–4

Ford Motor Company terms and acronyms.

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620 Appendix B Terms and Acronyms

DaimlerChrysler Term DaimlerChrysler Acronym OBD II Acronym

Actuator Test Mode ATM

Adaptive Fuel Control LTFT/STFT

Automatic Idle Speed AIS IAC

Automatic Shutdown relay ASD relay

Backpressure EGR BPEGR BPEGR

Barometric Pressure Read solenoid BARO Read

Charge Temperature sensor IAT sensor

Coolant Temperature Sensor CTS ECT sensor

Diagnostic Readout Box DRB I, II, III

Direct Ignition System DIS

Distance Sensor DS VSS

Electronic Lean Burn ELB

Electronic Spark Advance ESA

Electronic Spark Control ESC

Engine Control Unit ECU PCM

Exhaust Gas Recirculation EGR EGR

Heated Oxygen Sensor HO

S HO

Jeep/Truck Engine Controller JTEC

Knock Sensor KS KS

Manifold Absolute Pressure sensor MAP sensor MAP sensor

Mass Air Flow sensor MAF sensor MAF sensor

Next Generation Controller NGC

Oxygen Sensor O

S O

Power Loss Lamp PLL MIL

Sequential Fuel Injection SFI SFI

Single Board Engine Controller SBEC I, II, III, IIIa

Single Module Engine Controller SMEC

Throttle Body Injection TBI TBI

Throttle Position Sensor TPS TP sensor or TPS

Figure B–5

DaimlerChrysler Corporation terms and acronyms.

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Appendix B Terms and Acronyms 621

Nissan Term Nissan Acronym OBD II Acronym

Absolute Pressure Sensor MAP/BARO

Adaptive Fuel Control ALPHA LTFT/STFT

Auxiliary Air Control valve AAC valve IAC

Camshaft Position sensor PHASE CMP sensor

Crankshaft Position sensor REF/POS CKP sensor

Electronic Concentrated Control System ECCS

Engine Control Unit ECU PCM

Engine Coolant Temperature sensor ECT sensor ECT sensor

Exhaust Gas Recirculation EGR EGR

Heated Oxygen Sensor HO

S HO

Idle Air Control Valve IACV IAC

Intake Air Temperature sensor IAT sensor IAT sensor

Mass Air Flow sensor MAF sensor MAF sensor

Oxygen Sensor O

S O

Sequential Fuel Injection SFI SFI

Throttle Position Sensor TPS TP sensor or TPS

Figure B–6 Nissan terms and acronyms.

Toyota Term Toyota Acronym OBD II Acronym

Engine Control Unit ECU PCM

Engine Coolant Temperature sensor ECT sensor ECT sensor

Exhaust Gas Recirculation EGR EGR

Heated Oxygen Sensor HO

S HO

Intake Air Temperature sensor IAT sensor IAT sensor

Manifold Absolute Pressure sensor MAP sensor MAP sensor

Mass Air Flow sensor (air flow meter) MAF sensor MAF sensor

Oxygen Sensor O

S O

Sequential Fuel Injection SFI SFI

Throttle Position Sensor TPS TP sensor or TPS

Toyota Computer-Controlled System TCCS

Figure B–7

Toyota terms and acronyms.

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