1988 PONTIAC FIERO light

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-A-19
THIS CHART ASSUMES THERE IS NO
CODE
54
'OFF' FOR 10 SECONDS. AIC "OFF". ,,. . . . . . . . .'.
"ON". FUEL PUMP WILL RUN FOR ABOUT 2 : FROM :
THE IGNITIONMAY HAVE TO BE : A-3 : CYCLED "ON" MORE THAN ONCE
TO OBTAIN MAXIMUM PRESSURE.
ALSO, IT IS NORMAL FOR THE
PRESSURE TO DROP SLIGHTLY
WHEN THE PUMP STOPS.
AT NORMAL OPERATING
TEMPERATURE.
IGNITION "ON"
@ IGNITION "OFF".
BLOCK FUEL PRESSURE @ APPLY 12 VOLTS LINE BY PINCHING FLEX
TO FUEL PUMP
HOSE. PRESSURE TEST TERMINAL.
@ IGNITION "OFF" FOR 10 @ APPLY 10 INCHES OF VACUUM
LEAKING PUMP COUPLING
TO PRESSURE REGULATOR. @ IGNITION "ON".
INLET FILTER.

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-A-27
CKT410 SHORTED TO GROUND.
CKT410 SHORTED TO SENSOR GROUND CIRCUIT.
FAULTY ECM.
DIAGNOSTIC AID
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.
COOLANT
SENSOR
TEMPERATURE TO RESISTANCE VALUES
(APPROXIMATE)
"F "C OHMS
210 100 185
160 70 450
100 38 1,800
70 20 3,400
40 4 7,500
20 -7 13,500
0 -1 8 25,000
-40 -40 100,700

6E3-A-38 2.8b (VIM S) DRIVEABILITY AND EMISSIONS
FRONT VIEW OF CONNECTOR
MODE SIGNAL
5V REFERENCE
THRBmLE POSiT10N SENSOR (TPS) CIRCUIT
(SIGNAL VOLTAGE HIGH)
2.8L (VIN S) ""F-SERIES (PORT)
Circuit Description:
The throttle position sensor (TPS) provides a voltage signal that changes relative to the throttle blade.
Signal voltage will vary from about
.5 at idle to about 5 volts at wide open throttle.
The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the
ECM control outputs.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 21 will set if:
@ Engine is running
@ TPS signal voltage is greater than 2.5 volts
@ Air flow is less than 12 gmlsec.
All conditions met for 5 seconds.
OR
@ TPS signal voltage over 4.5 volts with ignition
"ON".
The TPS has an auto zeroing feature. If the
voltage reading is within the range of 0.35 to 0.7 volts,
the ECM will use that value as closed throttle.
If the
voltage reading is out of the auto zero range at closed
throttle, refer to "TPS Adjustment" in Section
"6E3-
C1".
2. With the TPS sensor disconnected, the TPS
voltage should go low if the
ECM and wiring is
OK.
3. Probing CKT 452 with a test light checks the 5volt
return circuit, because a faulty 5volt return will
cause a Code 21.
Diagnostic Aids:
A "SCAN" tool reads throttle position in volts.
Voltage should increase at a steady rate as throttle
is
moved toward WOT.
An open in CKT 452 will result in a Code 21.
Refer to "Intermittents" in Section "B".

DRlVEABlLlTV AND EMISSIONS 2.8L (VIN S) 6E3-A-31
CODE 21 IS INTERMITTENT. IF NO
ADDITIONAL CODES WERE STORED,
2 VOLTS (200mV). EFER TO "DIAGNOSTIC AIDS" ON
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

DRIVEABILITY AND EMISSIONS 2.8L (VIN %) 6E3-A-33
@ JUMPER CKTS416 &417 TOGETHER. IF
NO ADDITIONAL CODES WERE STORED, REFER TO
CONNECTED TO
12 VOLTS.
"SCAN" TOOL SHOULD DISPLAY TPS OVER
CKT416 OPEN. CKT 417 OPEN.
SHORTED TO GROUND. SHORTED TO
GROUND.
FAULTY CONNECTION. SHORTED TO
SENSOR GROUND CIRCUIT.
FAULTY ECM CONNECTION.
FAULTY ECM.
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

6E3-A-40 2.8L (VIN 5) DRIVEABILITY AND EMISSIONS
VENT FILTER
450 BLWHT ITCH SIGNAL -
CODE 32
EGR SYSTEM FAILURE
2.8L (VIN S) "F" "SERIES (PORT)
Circuit Description:
The EGR vacuum control uses an ECM controlled solenoid. The solenoid is normally closed and the vacuum
source is a ported signal. The ECM will turn the EGR "ON" and "OFF" (Duty Cycle) by grounding CKT
435.
The duty cycle is calculated by the ECM based on information from the coolant and mass airflow sensor and
engine rpm. The duty cycle should be
0% (no EGR) when in park or neutral, TPS input below a specified value,
or TPS indicating WOT
With the ignition
"ON", engine stopped, the EGR solenoid is de-energized unless the diagnostic terminal is
grounded. Code 32 means that the EGR vacuum diagnostic switch was closed during start-up, or that the switch was
not detected closed under the following conditions.
@ Coolant temperature greater than 80" C (176°F).
@ EGR duty cycle commanded by the ECM is greater than 55%.
@ TPS less than half throttle, but not at idle.
@ All conditions above must be met for 5 seconds.
If the switch is detected closed during start-up, or
, if the switch is detected open when the above conditions
are met, the "Service Engine Soon" light will remain "ON" unless the switch changes state.
Test Description: Numbers below refer to circled 3. 'Po this point the EGR solenoid and valve are OK
numbers on the diagnostic chart. and the following check will check the diagnostic
1. If the first step caused Code 32 to set, then the vacuutn switch portion of the system.
ECM has recognized a closed vacuum switch on
4. The diagnostic switch should close at about 2" of
start-up. This test will determine whether the
vacuum. With vacuum applied, the switch should
EGR vacuum diagnostic switch is the cause or if close and resistance go to near zero ohms and the
the wiring or the ECM is the cause. vacuum should hold.
2. With the ignition "ON", the solenoid should not be
energized and vacuum should not pass to the EGR
valve.

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-A-43
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.
OR
1 MINUTE
OR UNTIL CODE 33 SETS
REPLACE MAF SENSOR CODE
33
IS INTERMITTENT.
REFER TO "DIAGNOSTIC
AIDS"
ON FACING PAGE.

6E3-A-44 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
NlnF RELAY CONN.
BATTERY
+ -,
I.P. HARNESS CONNECTOR IS WAY. (FRONTVIEW)
I.. . . . . . ., 1. EllCE
a
GAGE
902
TO EGR
& MAF RELAY 7-29-87 CCP SOLENOIDS MAF
SENSOR
ENG.
GND.
MAF SENSOR CONNECTOR
ECM
CODE 34
MASS AIR FLOW (MAF) SENSOR CIRCUIT
(GMISEC LOW)
2.8L (VIN 5) "F" SERIES (PORT)
Circuit Description:
The MAF sensor measures the flow of air entering the engine. The sensor produces a frequency output
between 32 and 150 hertz
(3grnfsec to 150gndsec). A large quantity (high frequency) indicates acceleration, and
a small quantity (low frequency) indicates deceleration or idle. This information is used by the ECM for fuel
control and is converted by a "SCAN" tool to read out the air flow in grams per second. A normal reading is
about 4-7 grams per second at idle and increase with rpm.
The MAF sensor is powered up by the MAF sensor relay and the sensor should have power supplied to it
anytime the ignition is "ON".
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
I. Code 34 will set if:
@ Engine running
@ MAF sensor disconnected, faulty relay, or
MAF signal circuit shorted to ground.
OR
@ Air flow less than 2 grams per second (low
frequency).
A loose or damaged air duct can set Code 34.
This test checks to see if ECM recognizes a
problem.
A light "OFF" at this point indicates an
intermittent problem.
2. Checks to see if 5 volt reference signal from ECM
is at MAF
sensor harness connector.
3. Checks for 12 volt supply to MAF sensor.
4. Checks for open in 12 volt supply to relay.
Diagnostic Aids:
The "Scan" tool is not of much use in diagnosing
this code because when the code sets
gdsec will be
displaying the default value. However, the "Scan"
may be useful in comparing the signal of a problem
vehicle with that of a known good running one.
Check for loose or damaged air duct.
Inspect sensor and relay connections as an open
will result in
a Code 34.
Refer to "Intermittents" in Section "B".