check engine light PONTIAC FIERO 1988 Service Owner's Guide

CHARGING SYSTEM 6D3-1
SECTION 6D3
CHARG NG SYSTEM
CONTENTS
General Description ................................. 6D3- 1 Charging System ........................................ 6D3- 1
.......................................... Charging System - CS ............................... 6D3- 1 On-Car Service 6D3-2
................................................... Diagnosis .. 6D3- 1 Generator 6D3-3 ...................... ......................... ............................................. 6D3- 1 Specifications 6D3-3 Service Procedures .................................. Unit Repair .. 6D3-4-6 ............................... ............
GENERAL DESCRIPTION
The engine electrical system includes the battery,
ignition (primary and secondary), starter (and related
wiring) and the generator (and related wiring).
Diagnostic charts (see Section 6D) will aid in
trouble-shooting system faults. When a fault is traced
to a particular component, refer to that components'
section of the service manual.
CHARGING SYSTEM-CS
The CS Charging System has several sizes
available, including the CS-130 and CS-144. The
number (130 or 144) denotes the
OD in mm of the
stator laminations.
CS generators use a new type regulator and a
diode trio is not used. A delta stator, rectifier bridge,
and rotor with slip rings and brushes are electrically
similar to earlier generators. A conventional pulley and
fan is used and, on the CS-130, an internal fan cools the
slip ring end frame, rectifier bridge and regulator.
Unlike three-wire generators, the CS-130 and
CS-144 may be used with only two connections
-
battery positive and an "L" terminal to the charge
indicator bulb. Use of "P",
"F", and "S" terminals is
optional. The "P" terminal is connected to the stator,
and may be connected externally to
a tachometer or other
device. The
"F" terminal is connected internally
to field positive, and may be used as a fault indicator.
The "S" terminal may be connected externally to a
voltage, such as battery voltage, to sense voltage to be
controlled.
As on other charging systems, the charge
indicator lights when the switch is closed, and goes out
when the engine is running. If the charge indicator is
on with the engine running, a charging system defect
is indicated. For all kinds of defects, the indicator will
glow at full brilliance, not "half lit". Also, the charge
indicator will be on with the engine running if system
voltage is too high or too low. The regulator voltage
setting varies with temperature, and limits system
voltage by controlling rotor field current.
This regulator switches rotor field current on and
off at a fixed frequency of about 400 cycles per second.
By varying the on-off time, correct average field
current for proper system voltage control is obtained.
At high speeds, the on-time may be 10% and the
off-time 90%. At low speeds, with high electrical loads,
on-off time may be 90% and
lo%, respectively.
No periodic maintenance on the generator is
required.
DIAGNOSIS
SERVICE PROCEDURES
CHARGING SYSTEM
The generator does not require periodic
lubrication. The rotor shaft is mounted on ball bearings
at the drive end and roller bearings at the slip ring end.
Each contains a permanent grease supply. At periodic
intervals, check mounting bolts for tightness and adjust
belt tension (see Section
6B), if applicable.
e When adjusting belt tension, apply pressure at
center of generator, never against either end
frame.
GENERATOR BENCH CHECK-CS
To check generator in a test stand, remove as
specified in On-Car Service and proceed as follows: 1.
Make connections as shown in Figure
lH, except
leave the carbon pile disconnected. The ground
polarity of generator and battery must be the
same. The battery must be fully charged. Use a
30-500
OHM resistor between battery and "L"
terminal.
2. Slowly increase generator speed and observe
voltage.
3. If the voltage is uncontrolled and increases above
16.0 volts, the rotor field is shorted, the regulator
is defective, or both.
A shorted rotor field coil can
cause the regulator to become defective. NOTE:
The battery must be fully charged when making
this test.

IGNITION SYSTEM 6B4-3
flash-over, which causes engine misfiring. Do not
mistake corona discharge for flash-over, or a shorted
insulator. Corona is a steady blue light appearing
around the insulator, just above the shell crimp. It is
the visible evidence of a high-tension field and has no
effect on ignition performance. Usually it can be
detected only in darkness. This discharge may repel
dust particles, leaving a clear ring on the insulator just
above the shell. This ring is sometimes mistakenly
regarded as evidence that combustion gases have blown
out between shell and insulator.
lgnition Switch
The mechanical switch is located in the steering
column on the right hand side just below the steering
wheel. The electrical switching portion of the assembly
is separate from the key and lock cylinder. However,
both are synchronized and work in conjunction with
each other through the action of the actuator rod
assembly.
For a complete explanation of the key and lock
cylinder, and the actuator rod assembly, see
STEERING, Section
38. See Section 8 for electrical
switching.
DIAGNOSIS
IGNITION SYSTEM
Spark Plugs
Worn or dirty plugs may give satisfactory
operation at idling speed, but at higher RPM they
frequently fail. Faulty plugs are indicated in a number
of ways: poor fuel economy, power loss, loss of speed,
hard starting and generally poor engine performance.
Spark plugs may also fail due to carbon fouling,
excessive gap, or a broken insulator. Fouled plugs may
be indicated by black carbon
deposits. The black deposits are usually the result of
slow-speed driving and short runs, where sufficient
engine operating temperature is seldom reached. Worn
pistons, rings, faulty ignition, over-rich carburetion
and spark plugs which are too cold will also result in
carbon deposits.
Excessive gap wear, on plugs of low mileage,
usually indicates the engine is operating at high speeds,
or loads that are consistently greater than normal, or
that a plug which is too hot is being used. Electrode
wear may also be the result of plug overheating,
causcd
by combustion gases leaking past the threads due to
insufficient torquing of the spark plug. Excessively lean
carburetion will also result in accelerated electrode
wear.
Broken insulators are usually the result of
improper installation, or carelessness when regapping
the plug. Broken upper insulators usually result from
a poor fitting wrench, or an outside blow. The cracked
insulator may not show up right away, but will as soon
as oil or moisture penetrates the crack. The crack is
usually just below the crimped part of shell and may
not be visible.
Broken lower insulators usually result from
carelessness when regapping and generally are visible.
This type of break may result from the plug operating
too "hot", which may happen in periods of high-speed
operation or under heavy loads. When regapping a
spark plug, always make the gap adjustment by
bending the ground (side) electrode. Spark plugs with
broken insulators should always be replaced.
HE1 Distributor
See Unit Repair for distributor disassembly, test
and reassembly of individual distributor components,
when the distributor is removed from the vehicle. See
On-Car Service for distributor removal and installation
and for component removal with distributor in car. See
Section 6E for
HE1 and EST diagnosis.
SERVICE PROCEDURES
IGNITION SYSTEM
Distributor Ignition
NOTICE: This procedure is generally true for
most carlines. Where procedure is different, or
where additional information is required, see
"ON-CAR SERVICE" for specific
carline.
HE1 DISTRIBUTOR
Service Precautions
1. When making compression checks, disconnect
the ignition switch feed wire at the distributor.
When disconnecting this connector,
do not use
a screwdriver or tool to release the locking tab, as
it may break.
2. No periodic lubrication is required. Engine oil
lubricates the lower bushing and an oil-filled
reservoir provides lubrication for the upper
bushing. 3.
The tachometer (TACH) terminal is next to the
ignition switch (BAT) connector on the
distributor cap.
NOTICE: The tachometer terminal must
NEVER be allowed to touch ground, as damage
to the module and/or ignition coil can result.
Some tachometers currently in use may NOT be
compatible with the High Energy Ignition System.
Consult the manufacturer of the tachometer if
questions arise.
4. Dwell adjustment is controlled by the module,
and cannot be adjusted.
5. The material used to construct the spark plug
cables is very soft. This cable will withstand more
heat and carry a higher voltage, but scuffing and
cutting become easier. The spark plug cables
must be routed correctly to prevent
chafing or
cutting. See Spark Plug Section. When removing

IGNITION SYSTEM 6014.5
3. Rotor and cap. 4. Turn off the engine and remove the timing light.
Reconnect the number one spark plug wire, if
Set Ignition Timing removed.
Spark Plug Wires 1. Refer to the tune-up label located in the engine
compartment. Follow all instructions on the Use
care when removing spark plug wire boots
label. from
spark plugs. Twist the boot
1/2 turn before
removing and pull on the
boot only to remove the
With ignition off, connect the pick-up lead of
timing light to the number one spark plug. Use
a jumper lead between the wire and plug, or an
inductive type pick-up.
DO NOT pierce the wire,
or attempt to insert a wire between the boot and
the wire. Connect the timing light power leads
according to manufacturer's instructions.
Start the engine and aim the timing light at the
timing mark. The line on the balancer or pulley
will line up at the timing mark. If a change is
necessary, loosen the distributor hold-down
clamp bolt at the base of the distributor. While
observing the mark with the timing light, slighty
rotate the distributor until the line indicates the
correct timing. Tighten the hold-down bolt and
re-check the timing. wire.
When replacing plug wires, route the wires
correctly and through the proper retainers. Failure to
route the wires properly can lead to radio ignition noise
and crossfiring of the plugs, or shorting of the leads to
ground.
Special care should be exercised when reinstalling
spark plug boots, to assure that the metal terminal
within the boot is fully seated on the spark plug
terminal and that the boot has not moved on the wire.
If boot to wire movement has occurred, the boot will
give a false visual impression of being fully seated.
A
good check to assure that boots have been properly
assembled is to push sideways on the installed boots.
If they have been correctly installed, a stiff boot, with
only slight looseness, will be noted. If the terminal has
not been properly seated on the spark plug, only the
resistance of the rubber boot will be felt when pushing
sideways.
ON-CAR SERVICE
I I -COI L & BRACKET ASM. 2-DISTRIBUTOR 3-COIL WIRE I
Fig. 601 Distributor and Coil - LB8

8B-2 ENGINE ELECTRICAL
NO CRANKING, NO SOUND FROM SOLENOID
I TURN HEADLIGHTS AND DME LITE ON
TURN KEY TO START I
TEST BETTERY.
IF OK. REPAIR
.5 VOLT OR MORE a
OSITION, (POS. LEAD 0
GROUND CABLE CONN. ANDlOR REPLACE
CABLE.
CLEAN AND TIGHTEN
POS. BATTERY CABLE
TERMINALS
ANDlOR REPLACE CABLE. CONNECTOR.
FUSIBLE
CHECK CONNECTIONS
AND VOLTAGE AT
SOLENOID
"S' TERM.
LESS THAN
7 VOLTS b
FAULTY PURPLE WITH KEY IN START,
WIRE TO STARTER CHECK
VOLTAGE AT
G20201-6D
Fig. 1 Electrical System General Diagnosis - 1 of 2
GENERAL ELECTRICAL SYSTEM DIAGNOSIS 6D3 - Charging System
6D4
- ~~nitcon-§~stem Diagnosis and repair procedures for engine
6D5 - Engine Wiring
electrical subsystems are located in the following
subsections: Where a
"driveability" complaint
exists, or an
ECM code is set, go to Section
6E. Wiring diagrams,
6D
1 - Battery component locations and system checks are located in
6D2
- Cranking System Section 8A.

SECTION 6E2
TY AND EM
THIS SECTION APPLIES TO:
5.OL (VIN E) ""FYSERIES
CONTENTS
General Description .................... 5
Diagnostic Procedure ................... 5
SECTION A . DIAGNOSIIC CHARTS
Table of Contents ..................... A-1
Engine Components and Wiring
Component Location
................. A-2
Wiring Diagrams (1 of 3) .............. A-3
ECM Connector Terminal End View ...... A-6
Diagnostic Circuit Check ................. A-8
No "Service Eng~ne Soon" Light
Chart
A-1 .......................... A-10
No ALDL Data or Won't Flash Code 12
"Service Engine Soon" Light "ON" Steady
Chart A-2
.......................... A-1 2
Engine Cranks But Will Not Run
ChartA-3
(1 of 2) .................... A-14
Fuel System Diagnosis
ChartA-7(1 of 2) .................... A-18
Code 13-Oxygen Sensor Circuit (Open Circuit) . A-22
Code 14-Coolant Temperature Sensor Circuit
(HighTemperature Indicated) ........... A-24
Code 15-Coolant Temperature Sensor Circuit
(LowTemperature Indicated) .......... A-26
Code 21-Throttle Position Sensor (TPS) C~rcuit
(Signal Voltage High) ................ A-28
Code 22-Throttle Position Sensor (TPS) C~rcuit
(Signal voltage Low) ................. A-30
Code 23 Manifold Air Temperature (MAT) Sensor
. Circuit (Low Temp Indicated) .......... A-32
Code 43-Electronic Spark Control (ESC) Circuit . A46
Code 44-Oxygen Sensor Circu~t
(Lean Exhaust Indicated) .............. A-48
Code 45-Oxygen Sensor Circu~t
(Rich Exhaust Indicated) .............. A-50
Code 53 Vehicle Anti-Theft System
(VATS)
Circu~t ...................... A-52
Code 54-Fuel Pump Circuit (Low Voltage) .... A-54
Code 51 -PROM Error ................... A-56
Code 52-Calpak Error
(Faulty or Incorrect
Calpak) ............ A-56
Code 55-ECM Error ..................... A-56
SECTION B . SYMPTOMS
Table of Contents ..................... B-1
Before Starting ....................... B-1
Intermittents ......................... B-2
Hard Start ........................... 8-2
.................. Surges and/or Chuggle B-3
Lack of Power. Sluggish. or Spongy ......... 8-3
DetonationISpark Knock ................ 8-4
................ Hesitation. Sag. Stumble B-4
Cuts Out. Misses ....................... B-4
Poor Fuel Economy ..................... B-5
Rough. Unstable. or Incorrect Idle.
. Stalling ....................... ... B-5
Excessive Exhaust Emtss~ons or Odors ...... 8-6
Dieseling. Run-on ..................... 8-6
Backfire ............................. B-6
Restricted Exhaust System Check
Chart
B-1 .......................... 8-7
Code 24-Vehicle Speed Sensor (VSS) Circuit . . A-34
Code 25 Manifold Air Temperature (MAT) Sensor FUNCTIONAL CHECKS/
Circuit (High Temp . Indicated) .......... A-36 DIAGNOSqIC CHARTS
Code 32-Exhaust Gas Recirculat~on ParkINeutral Switch Diagnosis
........................ (EGR) Circuit ....................... A-38 Chart C- 1 A C1-12
Code 33-Manifold Absolute Pressure (MAP) Sensor Crank Signal
Circuit (Signal Voltage High-Low Vacuum)
. A-40 Chart C-1 B ........................ C1-14
Code %&Manifold Absolute Pressure (MAP) Sensor MAP
Output Check
......................... Circuit (Signal Voltage Low-High Vacuum) . A-42 ChartC-ID C1-16
Code 42-Electronic Spark Timing (EST) Circuit . A-44

6E2-2 5.OL (VIN El DRlVEABlLlTV AND EMISSIONS
Power Steering Pressure Switch (PSPS) Diagnosis
Chart C-1
E ......................... C1-18
ldle Air Control (IAC) Valve Check
Chart C-2C
......................... C2-16
Canister Purge Valve Check
Chart C-3
.......................... C3-4
Ignition System Check
Chart C-4
......................... C4-4
Electronic Spark Control (ESC) System Check
Chart C-5
.......................... C5-4
A.I.R. Management Check . Pedes Valve
Chart C-6
......................... C6-6
Exhaust Gas Recirculation (EGR) Check
Chart C-7
.......................... C7-4
Transmission Converter Clutch (TCC)
Electrical Diagnosis Chart C-8A
(1 of 2) ... C8-4
700-4R Transmission . Electrical Diagnosis
Chart C8-A
(2 of 2) ................... C8-6
Manual Transmission Shift Light Diagnosis
Chart
C-8B ........................ C8-8
SECTION C . COMPONENT SYSTEMS
Table of Contents .................... C-1
SECTION
C1
ELECTRONIC CONTROL MODULE AND SENSORS
GENERAL DESCRIPTION
............... C1-1
ELECTRONIC CONTROL MODULE (ECM) . . C1-1
PROM ........................... C1-1
CALPAK .......................... C1-2
ECMFUNCTION .................... C1-2
INFORMATION SENSORS ............. C1-2
Engine Coolant Temperature Sensor . . C1-2
MAP Sensor ...................... C1-2
MAT Sensor ...................... C1-3
Oxygen (Oz) Sensor ................ C1-3
Throttle Position Sensor (TPS) ........ C1-3
Knock Sensor .................... C1-4
Park Neutral Switch (Auto Only) ...... C1-4
Crank Signal ..................... C1-4
A/C Request Signal ............... C1-4
Vehicle Speed Sensor (VSS) ......... C1-4
Distributor Reference Signal ......... C1-4
(PSPS) ......................... C1-4
DIAGNOSIS ......................... C1-5
ECM ............................. C1-5
PROM ........................... C1-5
ECMINPUTS ....................... C1-5
Coolant Temperature Sensor ........ C1-5
MAT Sensor ...................... C1-5
MAP Sensor ...................... C1-6
Oxygen (Oz) Sensor ................ C1-6
Throttle Position Sensor (TPS) ........ C1-6
Vehicle Speed Sensor (VSS) ......... C1-6
P/N Switch ....................... C1-6
(PSPS) ......................... C1-6
A/C Request Signal ................ C1-6
......... Distributor Reference Signal C1-6
Knock Signal ................... C1-6
..................... ON-CARSERVICE C1-6
....... ELECTRONIC CONTROL MODULE C1-6
........................... PROM C1-7
Functional Check ................. C1-8
.......................... CALPAK C1-8
.................. COOLANTSENSOR C1-9
MAPSENSOR e..................... C1-9
OXYGEN (02) SENSOR ............... C1-9
THROTTLE POSITION SENSOR (TPS) ..... C1-10
PARKINEUTRAL SWITCH .............. C1-10
PARTS INFORMATION ................. C1-10
ParklNeutral Switch Diagnosis
Chart
C-1A ..................... C1-12
Crank Signal
Chart
C-1B ..................... C1-14
MAP Output check
Chart C-1 D
..................... C1-16
Power Steering Pressure Switch (PSPS) Diagnosis
ChartC-lE ..................... C1-18
SECTION C2
FUEL CONTROL SYSTEM
GENERAL DESCRIPTION
............... C2-1
PURPOSE ...*..................... C2-1
MODES OF OPERATION .............. C2-1
Starting Mode ................... C2-1
Clear Flood Mode ................ C2-2
RunMode ...................... C2-2
Open Loop ...................... C2-2
Closed Loop ..................... C2-2
Acceleration Mode ............... C2-2
Deceleration Mode ............... C2-2
Battery Correction Mode ........... C2-2
Fuel Cut Off Mode ................ C2-2
... FUEL CONTROL SYSTEM COMPONENTS C2-2
BASIC SYSTEM OPERATION ........... C2-3
THROTTLE BODY INJECTION (TBI) UNIT ... C2-3
Fuel Injectors .................... C2-3
Pressure Regulator ............... C2-3
.......... Idle Air Control (IAC) Valve C2-4
........ Throttle Position Sensor (TPS) C2-4
FUELPUMP ........................ C2-5
....... FUEL PUMP ELECTRICAL CIRCUIT C2-5
DIAGNOSIS
......................... C2-5
FUEL CONTROL .................... C2-5
......... Idle Air Control Valve (IAC) C2-5
Dr~veability ..................... C2-5
ON VEHICLE SERVICE
................. C2-5
...... GENERALSERVICE INFORMATION C2-5
Fuel Pressure Relief ............... C2-7
........... Fuel System Pressure Test C2-7
Cleaning and lnspect~on ........... C2-7
......... Thread Lockrng Compound C2-7

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-5
ALL NEW GENERAL MOTORS VEHICLES ARE CERTIFIED BY THE UNITED STATES
ENVIRONMENTAL PROTECTION AGENCY AS CONFORMING TO THE REQUIREMENTS OF THE
REGULATIONS FOR THE CONTROL OF AIR POLLUTION FROM NEW MOTOR VEHICLES.
THlS
CERTIFICATION IS CONTINGENT ON CERTAIN ADJUSTMENTS BEING SET TO FACTORY
STANDARDS. IN MOST CASES, THESE ADJUSTMENT POINTS EITHER HAVE BEEN
PERMANENTLY SEALED
AND/OR MADE INACCESSIBLE TO PREVENT INDISCRIMINATE OR
ROUTINE ADJUSTMENT IN THE FIELD. FOR
THlS REASON, THE FACTORY PROCEDURE FOR
TEMPORARILY REMOVING PLUGS, CAPS, ETC., FOR PURPOSES OF SERVICING THE PRODUCT,
MUST BE STRICTLY FOLLOWED AND, WHEREVER PRACTICABLE, RETURNED TO
THE
ORIGINAL INTENT OF THE DESIGN.
INTRODUCTION
GENERAL DESCRIPTION DIAGNOSIS PROCEDURE
This section applies to engines which have a fuel
injector mounted above a throttle body assembly. The
entire assembly is mounted to the intake manifold and
is referred to as "Throttle Body Injection".
These engines have controls to reduce exhaust
emissions, while maintaining good driveability and
fuel economy.
An engine control module
(ECM) is the heart of
this control system and has sensors used to provide
information about engine operation and the various
systems it controls. Details of basic operation,
diagnosis, functional checks, and on-vehicle service
are covered in Section
"C", Component Systems.
The
ECM has the ability to do some diagnosis of
itself, and of other parts of the system. When it finds a
problem,
it lights a "Service Engine Soon" light on the
instrument panel and a trouble code will be stored in
the ECM memory. This does not mean that the engine
should be stopped right away, but that the cause of the
light coming
"ON" should be checked as soon as
reasonably possible. The
following
sectionds) are written for specific
engine applications and are clearly indentified. Be
sure to use only the section which applies to the
engine family being diagnosed.
Before using this section of the manual, you
should be familiar with the information and the
proper diagnosing procedures as described in Section
"6E". If the proper diagnosis procedures are not
follo\l;red, as described in Section "6En, it may result in
unnecessary replacement of good parts.
Trouble tree charts incorporate diagnosis
procedures using an
ALDI, "Scan" tool, where
possible. The "Scan" tool has the ability to save time
in diagnosis and prevent the replacement of good
parts. The key to using; the "Scan" tool
successfully for diagnosis lies in the technician's
abilitv to understand the system
he is try in^ to
diagnose,
as well as an understanding of the
"Scan" tool's limitations. See Section
6E for more
information.

DRIVEABILITY AND EMISSIONS S.OL (VIN E) 6EZ-A-1
5.OL ENGINE
DIAGNOS"FC CIRCUIT CHECK Cold Oxygen Sensor
The "Diagnostic Circuit Check" verifies the On some engines. the oxygen sensor will cool off
system is functioning correctly
. Some special after only a short period of operation at idle . This will
considerations to keep in mind while making the
put the system into "Open Loop"
. To restore "Closed
"Diagnostic Circuit Check" are:
Loop" operation. run the engine at part throttle
several minutes and accelerate from idle to part
Blocking Drive Wheels throttle a few times .
The vehicle drive wheels should always be blocked BASIC PROCEDURE
while checking the system .
If you have not reviewed the basic information on
how to use the diagnostic procedures. go to the
introduction of this section
.
SECTION A
ENGINE COMPONENTS
/ WlRlNG DIAGRAMS 1 DIAGNOSTIC CHARTS
Component Locations ........................................................ Page A-2
Wiring Diagrams (1 of 3) ...................................................... Page A.3.4.5
ECM Connector Terminal End View .............................................. Page A-6
Diagnostic Circuit Check ...................................................... Page A-8
No "Service Engine Soon" Light. Chart A-1 ......................................... Page 14-10
No ALDL Data or Won't Flash Code 12. "Service Engine Soon" Light "ON" Steady. Chart A-2 ... Page A-I 2
Engine Cranks But Will Not Run . Chart A-3 (1 of 2) .................................. Page A-1 4
. Fuel System Diagnosis Chart A-7 (1 of 2) .......................................... Page A-1 8
Code 13 Oxygen Sensor Circuit (Open C~rcu~t) ...................................... Page A-22
Code 14 Coolant Temperature Sensor Circu~t (HighTemperature Indicated) ............... Page A-24
Code 15 Coolant Temperature Sensor Circu~t (LowTemperature Indicated) ............... Page A-26
Code 21 Throttle Position Sensor (TPS) Circu~t (S~gnal Voltage High) ...................... Page A-28
Code 22 Throttle Position Sensor (TPS) Circuit (Signal voltage Low) ..................... Page A-30
Code 23 Manifold Air Temperature (MAT) Sensor Circuit (Low Temp . Indicated) ............ Page A-32
Code 24 Vehicle Speed Sensor (VSS) Circuit ........................................ Page A-34
Code 25 Manifold Air Temperature (MAT) Sensor Circuit (High Temp . Indicated) ............ Page A-36
Code 32 Exhaust Gas Recirculation (EGR) Circuit .................................... Page A-38
Code 33 Manifold Absolute Pressure (MAP) Sensor Circuit (Signal Voltage High-Low Vacuum) . . Page A-40
Code 34 Manifold Absolute Pressure (MAP) Sensor Circuit (Signal Voltage Low-High Vacuum) . . Page A-42
Code 42 Electronic Spark Timing (EST) Circuit ...................................... Page A-44
Code 43 Electronic Spark Control (ESC) Circuit ...................................... Page A-46
Code 44 Oxygen Sensor Circuit (Lean Exhaust Indicated) .............................. Page A-48
Code 45 Oxygen Sensor Circuit (Rich Exhaust Indicated) .............................. Page A-50
Code 53 Vehicle Anti-Theft System (VATS) Circuit ................................... Page A-52
Code 54 Fuel Pump Circuit (Low Voltage) ......................................... Page A-54
Code 51 Code 51 PROM Error .................................................. Page A-56
Code 52 Calpak Error (Faulty or Incorrect Calpak) ................................... Page A-56
.......................................................... Code55ECMError PageA-56

6EZ-A-10 5.0L (VIN E) DRIVEABILITY AND EMISSIONS
TO OIL PRESS. SW.
&FUEL PUMP RELAY
BATTERY
12 V
. . . . . . . . FUSIBLE LINK 15 WAY
439 PNWBLK
419
BRNNVHT
SERIAL DATA
451
WHTIBLK
450 BLWHT
ALDL CONNECTOR
NO "SERVICE ENGINE SOON" "LIGHT
5.OL (VIN E) "F'" SERIES (TBI)
Circuit Description:
There should always be a steady "Service Engine Soon" light, when the ignition is "ON" and engine stopped.
Battery is supplied directly to the light bulb.
The electronic control module (ECM) will control the light and
turn it "ON" by providing a ground path through CKT 419 to the ECM.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Battery feed CKT 340 is protected by a
20amp in-
line fuse. If this fuse was blown, refer to wiring
diagram on the facing page of Code 54.
2. Using a test light connected to 12 volts, probe each
of the system ground circuits to be sure
a good
ground is present. See ECM terminal end view in
front of this section for ECM pin locations of
ground circuits.
Diagnostic Aids:
Engine runs ok, check:
@ Faulty light bulb
@ CKT419open
@ Gage fuse blown. This will result in no oil, or
generator lights, seat belt reminder, etc.
Engine cranks, but will not run.
@ Continuous battery - fuse or fusible link open.
@ ECM ignition fuse open.
@ Battery CKT 340 to ECM open.
o Ignition CKT 439 to ECM open.
@ Poor connection to ECM.

6E2-A-12 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
TO OIL PRESS. SW. ECM
&FUEL PUMP RELAY
FUSE
& HOLDER BATTERY 12 V . . . . . . . .
FUSIBLE LINK
439
PNWBLK
419 BRNNVHT
- -
451 WHTIBLK
450
BLWHT
ALDL CONNECTOR
8-4-87
55 1235-6E
CHART A-2
NO ALDL DAM OR WON"T FLASH CODE 12
'SERVICE ENGINE SOON" LLlGHT "ON" "STEADY
5.OL (VIN E) "F" "SERIES (TBI)
Circuit Description:
There should always be a steady "Service Engine Soon" light, when the ignition is "ON" and engine stopped.
Battery is supplied directly to the light bulb. The electronic control module
(ECM) will turn the light "ON" by
grounding CKT 419 at the ECM.
With the diagnostic terminal grounded, the light should flash
a Code 12, followed by any trouble code(s)
stored in memory.
A steady light suggests a short to ground in the light control CKT 419, or an open in diagnostic CKT 451.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. If there is a problem with the ECM that causes
a
"Scan" tool to not read serial data, then the ECM
should not flash a Code
12. If Code 12 does flash,
be sure that the "Scan" tool is working properly on
another vehicle. If the "Scan" is functioning
properly and CKT 461 is OK, the PROM or ECM
may
be at fault for the NO ALDL symptom.
2. If the light goes "OFF" when the ECM connector is
disconnected, then CKT 419 is not shorted to
ground.
3. This step will check for an open diagnostic CKT
45 1.
4. At this point, the "Service Engine Soon" light
wiring is OK. The problem is a faulty ECM or
PROM. If Code 12 does not flash, the ECM should
be replaced using the original PROM. Replace the
PROM only after trying an ECM, as a defective
PROM is an unlikely cause of the problem.