1988 PONTIAC FIERO Service Repair Manual

6E3-A-54 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
OXYGEN ( O2 ) SENSOR
CODE 44
OXYGEN SENSOR CIRCUIT
(LEAN EXHAUST INDICATED)
5.OL (VIN F) & 5.7L (VIN 8) '"F" "SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10
megohm digital voltmeter, this may read as low as .32 volts.) The
02 sensor varies the voltage within a range
of about 1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below about 360°C
(600°F). An open
sensor circuit or cold sensor causes "Open Loop" operation.
Test Description: Numbers below refer to circled @
numbers on the diagnostic chart.
1. Code 44 is set when the O2 sensor signal voltage @
on CKT 412.
@ Remains below .2 volt for 50 seconds.
@ And the system is operating in "Closed Loop".
@
Diagnostic Aids:
Using the "Scan", observe the block learn values at
different rpm and air flow conditions. The "Scan" also
displays the block cells, so the block learn values can
@
be checked in each of the cells to determine when the
Code 44 may have been set.
If the conditions for Code
44 exist, the block learn values will be around 150.
@ - 02 sensor wire. Sensor pigtail may be @
m~spositioned and contacting the exhaust
manifold.
@ Check for intermittent ground in wire between
connector and sensor.
@ MAF Sensor. A mass air flow (MAF) sensor @
output that causes the ECM to sense a lower than
normal air flow will cause the system to go lean.
Disconnect the
MAF sensor and, if the lean
condition is gone, replace the
MAF sensor. Lean
Iniector(s). Perform
injector balance test
CHART C-2A.
Fuel Contamination. Water,
even in small
amounts, near the in-tank fuel pump inlet can be
delivered to the injectors. The water causes a lean
exhaust and can set a Code 44.
Fuel Pressure. System will be lean if pressure is
too low.
It may be necessary to monitor fuel
pressure while driving the car at various road
speeds
and/or loads to confirm. See Fuel System
diagnosis CHART
A-7.
Exhaust Leaks. If there is an exhaust leak,
outside air can be pulled into the exhaust and past
the sensor. Vacuum or crankcase leaks can cause
a lean condition.
AIR System. Be sure air is not being directed to
the exhaust ports while in "Closed Loop". If the
block learn value goes down while squeezing air
hose to left side exhaust ports, refer to CHART
C-
6.
If the above are
OK, it is a faulty oxygen sensor.

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-A-55
IF NO ADDITIONAL CODES WERE
SENSOR BETWEEN .35 VOLTS AND .55 VOLTS (350
STORED, REFER TO "DIAGNOSTIC
mV AND 550 mV).
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

6E3-A-56 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
OXYGEN ( O2 )SENSOR
-
CODE 45
OXYGEN SENSOR CIRCUIT
(RICH EXHAUST INDICATED)
S.OL (VIN F) & 5.7L (VIN 8) ""F-ERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10
megohm digital voltmeter, this may read as low as .32 volts.) The
02 sensor varies the voltage within a range of
about 1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F). An open
sensor circuit or cold sensor causes "Open Loop" operation.
Test Description: Numbers below refer to circled @ Check for fuel contaminated oil.
numbers on the diagnostic chart.
@ HE1 Shielding. An open ground CKT 453
1. Code 45 is set when the
02 sensor signal voltage or
(ignition system reflow) may result in EMI, or
CKT 412.
induced electrical "noise". The ECM looks at this
@ Remains above .7 volt for 50 seconds; and in
"noise" as reference pulses. The additional pulses
"Closed Loop".
result in a higher than actual engine speed
@ Engine time after start is 1 minute or more.
signal. The ECM then delivers too much fuel,
@ Throttle angle greater than 2% (about .2 volts
causing system to go rich. Engine tachometer
above idle voltage) will also show higher than actual engine speed,
which can help in diagnosing this problem.
Diagnostic Aids: @ Canister purge. Check for fuel saturation. If full
of fuel, check canister control and hoses. See
Using the "Scan", observe the block learn values at canister
purge Section
"C3".
different rpm and air flow conditions. The "Scan" also @ MAF sensor. An output that causes the ECM to
displays the block cells, so the block learn values can sense
a higher than normal airflow can cause the
be checked in each of the cells to determine when the system
to go rich. Disconnecting the MAF sensor
Code 45 may have been set. If the conditions for Code will
allow the ECM to set a fixed value for the
45 exists, the block learn values will be around 115. sensor.
Substitute a different MAF sensor if the
@ Fuel Pressure. System will go rich if pressure is the
rich condition is gone while the sensor is
too high. The ECM can compensate for some disconnected.
increase. However, if it gets too high, a Code 45
@ Check for leaking fuel pressure regulator
may be set. diaphram
by checking vacuum line to regulator
Use the Fuel System diagnosis CHART A-7. for
fuel.
@ Rich
iniector. Perform injector balance test @ TPS. An intermittent TPS output will cause the
CHART C-2A.
system to go rich, due to a false indication of the
@ Leaking injector. See CHART A-7. engine
accelerating.

DRIVEABILITY AND EMISSIONS 5.OL (VIN IF) & 5.7L (VIN 8) 6E3-A-57
HARNESS CKT412 TO GROUND. NO
ADDITIONAL CODES WERE
.35 VOLTS (350 mV).
CLEAR CODES ANDCONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

6E3-A-58 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
PNKIBLK 439
PPL 963
5V
IP CONN.
DECODER
MODULE
CODE 46
VEHICLE ANTI-THEFT SYSTEM (VATS) CIRCUIT
5.OL (VIN F) & 5.7L (VIN 8) 'TF'3SERlES (PORT)
Circuit Description:
The VATS system is designed to disable vehicle operation if the incorrect key or starting procedure is used.
The VATS decoder module sends a signal to the ECM if the correct key is being used. If the proper signal does
not reach the ECM on CKT 963, the ECM will not pulse the injectors
"ON" and thus not allow the vehicle to be
started.
Code
46 will set, if the proper signal is not being received at ECM terminal "B6" when the ignition is turned
"ON". Code 46 does not store in the ECM memory but is only present when the conditions stated above are met.
Test Description: Numbers below refer to circled 2. If Code 46 is stored, and the engine will not crank,
numbers on the diagnostic chart. it indicates that there is a VATS problem or an
1. If the engine cranks, and a Code 46 is stored, it incorrect key or starting procedure is being used.
indicates that the portion of the module which
generates the signal to the ECM is not operating
or CKT 963 is open or shorted to ground. If the
decoder module is found to be
OK, as determined
from Section
"8AV, the ECM may be at fault, but
this is not a likely condition.

DRIVEABILITY AND EMISSIONS 5.OL (WIN F) & 5.7L (VIN 8) 6E3-A-59
I @ IGNITION "ON". I
PROBLEM IS INTERMITTENT. IF NO
OTHER CODE IS STORED, REFER TO
TO GROUND IN CKT
963.
IF OK, IT IS A FAULTY VATS
DECODER MODULE.

6E3-A-60 .5.0L (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
340 - ORN
BULKHEAD CONN.
RELAY DRIVE
CODE 54
FUEL PUMP CIRCUIT
(LOW VOLTAGE)
5.OL (VIN F) & 5.7L (VIIN 8) "F" WRIES (PORT)
Circuit Description:
The status of the fuel pump CKT 120 (PPSW) is monitored by the ECM at terminal "H2" and is used to
compensate fuel delivery based on system voltage. This signal is also used to store a trouble code if the fuel
pump relay is defective or fuel pump voltage is lost while the engine is running. There should be about 12 volts
on CKT
120 for 2 seconds after the ignition is turned "ON", or any time references pulses are being received by
the ECM.
Code
54 will set, if the voltage at terminal "R2" is less than 2 volts for 1.5 seconds since the last reference
pulse was received. This code is designed to detect a faulty relay, causing extended crank time, and the code
will help the diagnosis of an engine that
"CRANKS BUT WILL NOT RUN".
If a fault is detected during start-up, the "Service Engine Soon" light will stay "ON" until the ignition is
cycled "OFF". However, if the voltage is detected below
2 volts, with the engine running, the light will only
remain "ON" while the condition exists.

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-A-61
ONNECT FUEL PUMP
E LIGHT WITHIN 2
@ OIL PRESSURE NORMAL.