1988 PONTIAC FIERO fuse chart

6E3-A-92 2.8b (VIN SI DRIVEABILITY AND EMISSIONS
TO OIL PRESS. SW.
&FUEL PUMP RELAY
FUSE
& HOLDER BATTERY 12
V
.. am.. . FUSIBLE LINK 15 WAY
439
PNWBLK
- 419 BUNNVHT
SERIAL DATA
451
WHTIBLK
450 BLWHT
ALDL CONNECTOR
CHART A-2
NO ALDL OR WONT FLASH CODE 12
""SERVICE ENGlNE SOON" MGHT ""8N13SPEADY
2.8L (VIN S) ""FYSERlES (PORT)
Circuit Description:
There should always be a steady "Service Engine Soon" light when the ignition is "ON" and engine stopped.
Battery ignition voltage is supplied 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, the ECM
should not flash a Code 12. If Code 12 is flashing
check for CKT
451 short to ground. 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
AL,DI,
symptom.
2. If
the light goes "OFF" when the ECM connector is
disconnected, CKT 419 is not shorted to ground.
3. This step will check for an open diagnostic CKrl'
451.
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
he replaced using the original PROM. Replace the
PROM only after trying an ECM, as a defective
PROM is an unlikely cause of the problem.
Diagnostic Aids:
Solenoids and relays are turned "ON" or "OFF" by
the ECM using internal electronic switches called
"drivers". Each driver is part of a group of four called
"Quad-l)rivers". Failure of one driver can damage
any other driver in the set.
Hefore replacing ECM, be sure to check the coil
resistance of
all solenoids and relays controlled by the
14:CM. Set: I':C%f wiring cliugrntn for the solcnoid(s)
.c~~cl rel;~ (-1 ~ititl lllc coil tcrtriitlul itlentilication.

6E3-A-22 2.8L (VlN S) DRIVEABILITY AND EMISSIONS
COLD START FUEL INJECTION
SWITCH CONNECTOR
TO NEUTRAL START SWITCH
OR CLUTCH START SWITCH
- - COLD START FUEL
- CLOSED BELOW 35°C.
8 SEC. TIME LIMIT
COOLANT
CHART A-9
COLD START VALVE
2.8b (VIN S) ""FYSERIES (PORT)
Circuit Description:
The cold start valve is used to provide additional fuel during the crank mode to improve colt1 start-ups. This
circuit is important when engine coolant temperature is low because the other injectors are not pulsed
"ON"
long enough to provide the needed amount of fuel to start.
The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and
is protected by a fuse. The system is controlled by
a cold start fuel injection switch which provides a ground path
for the valve during cranking when engine coolant is below
95°F (35°C).
The cold start fuel injection switch consists of a bimetal material which opens at a specified coolant
temperature. This bimetal is also heated by the winding in the switch which allows the valve to stay
"ON" for 8
seconds at -20°C (-5°F) coolant. The time the switch will stay closed varies inversely with coolant temperature.
In other words, as the coolant temperature goes
LIP, the cold start valve "ON" time goes down.
Pest Description: Numbers below refer to circled The amount of pressure drop depends on the
numbers on the diagnostic chart.
temperature of the engine.
1. Disconnecting the distributor 4-way connector 2. This test will determine the continuity through
will disable the other injectors. the switch to ground.

6E3-B-2 2.8L (VIN 5) DRIVEABILITY AND EMISSIONS
Problem may or may not turn "ON" the "Service Engine SoonJ' light, or store a code.
DO NOT use the trouble code charts in Section
"A" for intermittent problems. The fault must be
present to locate the problem. If a fault is
intermittent, use of trouble code charts may result
in replacement of good parts.
@ Most intermittent problems are caused by
faulty electrical connections or wiring. Perform
careful check as described at start of Section
"B". Check for:
@ Poor mating of the connector halves, or
terminals not fully seated in the connector
body (backed out).
@ Improperly formed or damaged terminals.
All connector terminals in problem circuit
should be carefully reformed to increase
contact tension.
@ Poor terminal to wire connection. This
requires removing the terminal from the
connector body to check. See "Introduction"
to Section
"6E".
@ If a visual check does not find the cause of the
problem, the car can be driven with a voltmeter
connected to a suspected circuit. A "Scan" tool
can also be used for monitoring input signals to
the ECM to help detect intermittent conditions.
An abnormal voltage, or "Scan" reading, when
the problem occurs, indicates the problem may
be in that circuit. If the wiring and connectors
check OK and a trouble code was stored for a
circuit having a sensor, except for Codes
43, 44,
and 45, substitute a known good sensor and
recheck. An
intermittent "Service Engine Soon" light
with no stored code may be caused by:
@ Ignition coil shorted to ground and arcing at
spark plug wires or plugs.
@ "Service Engine Soon" light wire to ECM
shorted to ground. (CKT 419).
@ Diagnostic "Test" terminal wire to ECM,
shorted to
ground.(CKT 451)
@ ECM power grounds. See ECM wiring
diagrams.
@ Loss of trouble code memory. To check,
disconnect TPS and idle engine until "Service
Engine Soon" light comes "ON". Code
22 should
be stored, and kept in memory when ignition is
turned "OFF". If not, the ECM is faulty.
@ Check for an electrical system interference
caused by a defective relay, ECM driven
solenoid, or switch. They can cause
a sharp
electrical surge. Normally, the problem will
occur when the faulty component is operated.
@ Check for improper installation of electrical
options, such as lights, 2-way radios, etc.
@ EST wires should be kept away from spark plug
wires, distributor wires, distributor housing,
coil, and generator. Wire from ECM to
distributor (CKT
453) should be a good
connection.
@ Check for open diode across A/C compressor
clutch, and for other open diodes (see wiring
diagrams).
HARD START
Definition: Engine cranks OK, but does not start for a long
time. Does eventually run, or may start hut immediately dies.
@ Perform careful check as described at start of -
Section "B".
@ Make sure driver is using correct starting
procedure.
@ CHECK:
- TPS for sticking or binding or a high TPS
voltage with the throttle closed (should read
less than
,700 volts).
- High resistance in coolant sensor circuit or
sensor itself. See Code 15 chart or with
a.
"Scan" tool compare coolant temperature with
ambient temperature on
a cold engine. 8
- Fuel pressure CHART A-7. Water contaminated
fuel.
EGR operation. Be sure valve seats properly and
is not staying open. See CHART C-7.
Both injector fuses (visually inspect).
Ignition system
- Check distributor for:
Proper output with ST-125.
Worn shaft.
Bare and shorted wires.
Pickup coil resistance and connections.
Loose ignition coil ground.
Moisture in distributor cap.
If problem exists in cold weather, check cold start
valve. See CHART A-9.

6E3-Cl-4 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
BarWNeutral Switch (Auto Only)
The ParWNeutral (PIN) switch indicates to the
ECM when the transmission is in Park or Neutral.
This information is used for the TCC and the IAC
valve operation.
Important
Vehicle should not be driven with ParWNeutral
switch disconnected as idle quality will be affected
and a possible false Code
24 (VSS).
See Section "$A" for more information on the PIN
switch, which is part of the neutrallstart and backup
light switch assembly.
NC '"n" Signal
This signal tells the ECM that the A/C selector
Switch is turned on, and that the pressure cycling
switch is closed. The ECM uses this to adjust the idle
Speed when the air conditioning is working.
If this signal is not available to the ECM, idle may
be rough, especially when the
A/C compressor cycles.
The voltage at ECM terminal "B8" should equal
battery voltage when
AIC is requested and the
pressure cycling switch is closed.
The signal at
B8 will cause the ECM to turn on the
A/C clutch by energizing the A/C relay.
Distributor Reference Signal
The distributor sends a signal to the ECM to tell it
both engine RPM and crankshaft position. See EST
System for further information.
To read the codes, use a "Scan" tool or ground the
diagnostic terminal with the engine not running and
the ignition on. The "Service Engine Soon" light will
flash Code 12 three times and
then flash each code
stored in memory three times. All codes stored in
memory would have been read when Code 12 was
flashed again. No new codes can be stored when in the
Diagnostics Mode (diagnostics lead grounded).
This
eliminates confusion while the system is being worked
on. To clear the codes from memory:
@ Ignition off
@ Remove fuse located in a weather proof holder
located near the battery for 30 seconds.
Since the ECM can have
a failure which may
effect only one circuit, following the Diagnostic
Procedures in this section will determine which circuit
has a problem and where it is. If
a diagnostic chart indicates that the ECM
connections or ECM is the cause of
a problem and the
ECM is replaced, but does not correct the problem, one
of the following may be the reason:
€9
connections. - The diagnostic chart will say "ECM
connections or ECM. The terminals may have to be
removed from the connector in order to check them
properly.
@ The ECM or PROM is not correct for the
application.
- The incorrect components may cause a
malfunction and may or may not set a code.
@ The problem is intermittent. - This means that
the problem is not present at the time the system is
being checked. In this case, refer to the "Symptoms"
portion of the manual and make a careful physical
inspection of all portions of the system involved.
@ Shorted solenoid, relay coil, or harness. -
Solenoids and relays are turned "ON" and "OFF" by
the
ECM,using internal electronic switches called
"Drivers". Each driver is part of
a group of four called
"Quad-drivers". Failure of one driver can damage any
other driver in the set.
Solelloid and relay coil
resistance must measure more than 20 ohms. Less
resistance will cause early failure of the ECM
"driver". A shorted solenoid, relay coil, or harness,
with a GMP4 computer, will not damage the ECM, but
will cause the component to be inoperative.
Before replacing an ECM, be sure to check the coil
resistance of all solenoids and relays controlled by the
ECM. See ECM wiring diagram for the
solenoid(s)
and relay(s) and the coil terminal identification.
534636 or BT 8405 testers or equivalent provide
a fast, accurate means of checking for a shorted coil or
a short to battery voltage.
@ The PROM may be faulty. - Although these
rarely fail, it operates as part of the ECM. Therefore,
it could be the cause of the problem. Substitute a
known good PROM.
@ The replacement ECM may be faulty. - After the
ECM is replaced, the system should be rechecked for
proper operation. If the diagnostic chart again
indicates the ECM is the problem, substitute
a known
good ECM. Although this is a rare condition, it could
happen.
ECM
A faulty ECM will be determined in the diagnostic
charts or
by a Code 55.
PROM
A faulty PROM may result in a Code 51.

TO MAF SENSOR
POWER & BURN-OFF
RELAY, OIL PRESS. SW.
.....-
439 PNKIBLK
419 BRNNVHT
SERIAL DATA
451 WHTIBLK
450
BLWHT
ALDL CONNECTOR
CHART A - 1
NO "'SERVICE ENGINE SOON" LIGHT
5.OL (VIN F) & 5.7L (VIN 8) "F'XSEBIE'S (PORT)
Circuit Description:
There should always be a steady "Service Engine Soon" light when the ignition is "ON" and engine stoppccl.
Ignition voltage 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. If the fuse in holder is blown, refer to facing page
of Code
54 for complete circuit.
2. Using a test light connected to 12 volts probe each
of the system ground circuits to be sure a good
ground is present. Refer to the ECM terminal end
view in front of this section for ECM pin locations
of ground circuits.
Diagnostic Aids:
Engine runs OK, check:
r Faulty light bulb.
@ CKrI' 419 open.
@ Gage fuse blown. This
will result in no oil or
generator lights, seat belt reminder, etc.
Engine cranks but will not run, check:
r Continuous battery - fuse or fusible link open.
@ ECM ignition fuse open.
r Battery CKT 340 to ECM open.
@ Ignition CKT 439 to ECM open.
@ Poor connection to ECM.

6E3-A-14 5.0L (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
CHART A-3
(Page 1 of 2)
ENGINE CRANKS BUT WON'T RUN
5.OL (VIN F) & 5.7L (VIN 8) "F" SRIES (PORT)
Circuit Description :
This chart assumes that battery condition and engine cranking speed are OK, and there is adequate fuel in
the tank.
Test Description: Numbers below refer to circled Diagnostic Aids:
numbers on the diagnostic chart.
1. A "Service Engine Soon" light "ON" is a basic test @ An EGR valve sticking open can cause a low
to determine if there is a
12 volt supply and airlfuel ratio during cranking. Unless
engine
ignition
12 volts to ECM. No ALDL may be due to enters
"Clear Flood" at the first indication of a
an ECM problem and CHART
A-2 will diagnose flooding
condition, it can result in a no start.
the ECM. If TPS is over
2.5 volts the engine may @ Check for fouled plugs.
be in the clear flood mode which will cause
@ A defective cold start circuit or water in fuel line
starting problems. The engine
will not start can
cause a no start in cold weather. See
CHART
without reference pulses and therefore the "Scan" A-9.
should read rpm (reference) during crank. @ A defective MAF Sensor may cause a no start or a
2. No spark may be caused by one of several stall
after start. To determine if the sensor is
components related to the Ignition System. causing
the problem, disconnect it. The
ECM will
CHART C-4 will address all problems related to then
use a default value for the sensor, and if the
the causes of a no spark condition. condition
is corrected and the connections are
OK,
3. The test light should blink, indicating the ECM is replace the sensor.
controlling the injectors ok. How bright the light
@ rllso check that injectors on both sides of engine
blinks is not important. However, the test light
will cause a test light to "blink". If not OK, check
should be a
5-34730-3 or equivalent. injector fuses.
4. Use fuel
pressure gage 5-34730-1 or equivalent. If al~ove are all OK, refer to "Symptoms" it1
Wrap a shop towel around the fuel pressure tap to Scction "R". Ilard Start.
absorb any small amount of fuel leakage that may
occur when installing the gage.

6E3-A-22 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
COLD START SWITCH
CONNECTOR
CLOSED BELOW
3S°C.
8 SEC. TIME LIMIT
COOLANT
CHART A99
COLD START VALVE CIRCUIT TEST
5.OL (VIN F) & 5.7L (VIN 8) "F" SERIES (PORT)
Circuit Description:
The cold start valve is used to provide additional fuel cluring the crank mode to improve cold start-ups. This
circuit is important when engine coolant temperature is low because the other injectors are not pulsed
"ON"
long enough to provide the needed amount of fuel to start.
The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and
is protected by a fuse. The system is controlled by a cold start fuel injection switch which provides a ground path
for the valve during cranking when engine coolant is below 35°C (95°F).
The cold start fuel injection switch consists of a bimetal material which opens at a specified coolant
temperature. This bimetal is also heated by the winding in the thertnal switch which allows the valve lo stay
"ON" for 8 seconds at -20°C (-4°F) coolant. The time the switch will stay closed varies inversely with coolant
temperature. In other words, as the coolant temperature goes up, the cold start valve
"ON" time goes down.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Disconnecting the distributor 4-way connector
will disable the other injectors. The amount of
pressure drop depends on the temperature of the
engine. This test could also be performed
by
removing the two injector fuses.
2. This test will determine the continuity through
the switch to ground.

6E3-B-2 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
Problem may or may not turn "ON" the "Service Engine Soon" light, or store a code.
DO NOT use the Trouble Code Charts in
An intermittent "Service Engine Soon" light
Section A for intermittent problems. The fault must
with no stored code may be caused by:
be present to locate the problem. If a fault is
@ Ignition coil shorted to ground and arcing at
intermittent, use of Trouble Code Charts
may result
spark plug wires or plugs.
in replacement of good parts.
"Service Engine Soon" light wire to
ECM
@ Most intermittent problems are caused by
shorted to ground. (CKT 419).
faulty electrical connections or wiring. Perform
Diagnostic "Test" Terminal wire to ECM,
careful check as described at start of Section
shorted to
ground.(CKT 451)
"B". Check for:
@ ECM power grounds. See ECSI wiring
@ Poor mating of the connector halves, or diagrams.
terminals not fully seated in the connector
@ Loss of trouble code memory. To check,
body (backed out). disconnect TPS and idle engine until "Service
@ Improperly formed or damaged terminals.
Engine Soon" light comes on. Code 22 should be
All connector terminals in problem circuit
stored, and kept in memory when ignition is
should be carefully reformed or replaced to turned "OFF". If not, the ECM is faulty.
insure proper contact tension.
@ Check for an electrical system interference
@ Poor terminal to wire connection. This caused by a defective relay, ECM driven
requires removing the terminal from the
solenoid, or switch. They can cause a sharp
connector body to check. See "Introduction"
electrical surge. Normally, the problem will
to Section
"6E". occur when the faulty component is operated.
@ If a visual check does not find the cause of the @ Check for improper installation of electrical
problem, the car can be driven with a voltmeter
options, such as lights,
%way radios, etc.
connected to
a suspected circuit. A "Scan" tool
EST wires should be kept away from spark plug
can also be used for monitoring input signals to wires, distributor wires, distributor housing,
the ECM to help detect intermittent conditions. coil, and generator. Wire from
ECM to
An abnormal voltage, or "Scan" reading, when distributor
(CKT 453) should be a good
the problem occurs, indicates the problem
may connection.
be in that circuit. If the wiring and connectors
@ Check for open diode across AIC compressor
check OK and a Trouble Code was stored for a
clutch, and for other open diodes (see wiring
circuit having a sensor, except for Codes
43, 44, diagrams).
and 45, substitute a known good sensor and
recheck.
HARD START
Definition: Engine cranks OK, but does not start for a long
time. Does eventually run, or may start but immediately dies.
Perform careful check as described at start of
Section
"B".
@ Make sure driver is using correct starting
procedure.
@ CHECK:
- TPS for sticking or binding or a high TPS
voltage with the throttle closed (should read
less than
.700 volts).
- High resistance in coolant sensor circuit or
sensor itself. See Code 15 chart or with
a
"Scan" tool compare coolant temperature with
ambient temperature on a cold engine.
- Fuel pressure CHART A-7.
- Water contaminated fuel.
- EGR operation. Be sure valve seats properly and
is not staying open. See CHART C-7.
- Both injector fuses (visually inspect).
- Ignition system - Check distributor for:
Proper Output with ST-125.
Worn shaft.
Bare and shorted wires.
Pickup coil resistance and connections.
Loose ignition coil ground.
Moisture in distributor cap.
@ If problem exists in cold weather, check cold start
valve. See CHART A-9.