1988 PONTIAC FIERO check engine

6EZ-A-34 5.OL (WIN E) DRIVEABILITY AND EMISSIONS
ECM
I.P.
8RN 437
K 7 PIN SIGNAL
PIN SWITCH
r ELK450 12v
1 CLOSED IN - 15- WAY .I.P. CONNECTOR - - PARK OR NEUTRAL I
CODE 24
VEHICLE SPEED SENSOR (VSS) CIRCUIT
5.OL (VIN E) "F" SERIES (TBI)
Circuit Description:
The ECM applies and monitors 12 volts on CKT 437. CKT 437 connects to the vehicle speed sensor which
alternately grounds CKT
437'when drive wheels are turning. This pulsing action takes place about 2000 times I
per mile and the ECM will calculate vehicle speed based on the time between "pulsesJ'.
A "Scan" reading should closely match with speedometer reading with drive wheels turning.
I
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 24 will set if:
@ CKT 437 voltage is constant.
@ Engine speed is between 1400 and 3600 rpm.
@ Less than 2% throttle opening.
@ Low load condition.
@ Not in park or neutral.
@ All conditions must be met for 4 seconds.
These conditions are met during a road load
deceleration.
2.
A voltage of less than 1 volt, at the 15-way
connector indicates that the CKT 437 wire
may be
shorted to ground.
Disconnect CKT 437 at the
vehicle speed sensor buffer. If
voltage remains less than 10 volts, then CKT
437 wire is grounded or open.
If 437 is not
grounded or open, check for a faulty
KCYI
connector or ECM.
Diagnostic Aids:
If "Scan" displays vehicle speed, check
parWneutra1 switch CHART C-LA on vehicle with
auto trans.
If switch is OK, check for intermittent
connections.
An open or short to ground in CKT 437
will result in
a a Code 24. Refer to Section "$A" for
col~lplete wiring diagram.
Refer to
"[ntermittents" in Section "B".

CODE 25
MANIFOLD AIR TEMPERATURE (MAn SENSOR CIRCUIT
(HIGH TEMPERATURE INDICATED)
5.OL (VIN E) ""FYOERIES (TBI)
Circuit Description:
The manifold air temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM
applies a voltage
(4-6) on CKT 472 to the sensor. When manifold air is cold, the sensor (thermistor) resistance is
high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance hecomes less,
and the voltage drops.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 25 will set if:
@ Signal voltage indicates a manifold air
tetnperature greater than 150°C
(302"F) for 2
seconds.
@ Time since engine start is 1 minute or longer.
Diagnostic Aids:
A "Scan" tool reads temperature of the air
entering the engine and should read close to ambient
air tetnperature when engine is cold, and rise as
underhood temperature increases.
Check harness routing for possible short to ground
in C KT
472.
Refer to "Intermittents" in Section "B".

6EZ-A-38 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
TO EGR VALVE
CODE 32
EXHAUSWAS RECIRCULATION (EGR) CIRCUIT
5.OL (VIN E) "FF" SERIES (TBI)
Circuit Description:
The ECM operates a solenoid to
control the exhaust gas recirculation (EGR) valve. This solenoid is
normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass
to the EGR valve.
The ECM monitors EGR effectiveness by de-energizing the EGR control solenoid thereby shutting off
vacuum to the EGR valve diaphragm. With the EGR valve closed, manifold vacuum will be greater than it was
during normal EGR operation and this change will be relayed to the ECM by the MAP sensor. If the change is
not within the calibrated window, a Code
32 will be set.
The ECM will check EGR operation when:
@ Vehicle speed is above 50 mph.
@ Engine vacuum is between 40 and 51 kPa.
@ No change in throttle position while test is being run.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Checks for solenoid stuck open.
2. Checks for solenoid always being energized.
3. Grounding test terminal should energize solenoid
and vacuum should drop.
4. Negative backpressure valve should hold vacuum
with engine "OFF".
5. When engine is started, exhaust backpressure
should cause vacuum to bleed off and valve to fully
close.
6. 5.OL engines have a ~nanifold vacuum source
which should have at least
7" Hg at idle.
Diagnostic Aids:
Vacuum lines should be thoroughly checked for
internal restrictions. The ECM uses the MAP sensor
for checking EGR operation. If there is a question of
MAP sensor accuracy use
CHART C-1D MAP output
check in Section "C".
If no problems are found refer to "Intermittents"
in Section
"13".

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-A-39
BEFORE USING THIS CHART, CHECK FOR MANIFOLD VACUUM TO EGR
@ GROUND DIAGNOSTIC TERMINAL. @ INSTALL A HAND HELD VACUUM PUMP WITH GAGE TO MANIFOLD
PUMP TO EGR VALVE.
@ USING A MIRROR,
OBSERVE EGR
DIAPHRAGM WHILE
APPLYING VACUUM.
DIAPHRAGM SHOULD OR
TERMINALS.
MOVE FREELY AND "ON",
ENGINE "OFF".
HOLD VACUUM FOR AT T
SHOULD LIGHT.
LEAST
20 SECONDS.
OBSERVE VACUUM GAGE ON
VACUUM PUMP.
HAS MOVED TO SEATED POSITION
CLEAR CODES AND CONFIRM "CLOSED LOOP"
OP

6EZ-A-40 5.0L (WIN E) DRIVEABILITY AND EMISSIONS
CODE 33
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL VOLTAGE HIGH - LOW VACUUM)
5.OL (VIN E) "F" SERIES (TBI)
Circuit Description:
The manifold absolute pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The
ECM receives this information as a signal voltage that will vary from about
1-1.5 volts at idle to 4-4.5 volts at
wide open throttle.
A "Scan" displays manifold pressure in volts. Low pressure (high vacuum) reads
a low voltage while a high
pressure (low vacuum) reads a high voltage.
If the MAP sensor fails the ECM will substitute
a fixed MAP value and use the throttle position sensor
(TPS) to control fuel delivery.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 33 will set when:
@ Signal is too high, (kPa greater than 68 kPa),
for a time greater than 5 seconds.
-S TPS less than 4%.
Engine misfire or a low unstable idle may set Code
33. Disconnect MAP sensor and system will go
into backup mode. If the misfire or idle condition
remains, see "Symptoms" in Section "B".
2. If the ECM recognizes the low MAP signal, the
ECM and wiring are OK.
Diagnostic Aids:
An open in CKT 455 will result in a Code 33.
With the ignition "ON" and the engine stopped,
the manifold pressure is equal to atmospheric
pressure and the signal voltage will be high.
This
information is used by the ECM as an indication of
vehicle altitude
and is referred to as BARO.
Comparison of this
BARO reading with a known good
vehicle with the same sensor is a good way to check
accuracy of a "suspect" sensor. Reading should he the
same,
& .4 volt.
Also
CHART C-lD can be used to test the MAP
sensor.
Refer to
"Intermittnets" in Section "B".
If idle is rough or unstable refer to "Symptoms" in
Section
"B" for items which can cause an unstable
idle.

6EZ-A-42 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
CODE 34
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL VOLTAGE LOW - HIGH VACUUM)
5.OL (VIN E) ""F-SERlES (TBI)
Circuit Description:
The manifold absolute pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The
ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5 volts at
wide open throttle.
If the MAP sensor fails the ECM will substitute a fixed MAP value and use the throttle position sensor
(TPS) to control fuel delivery.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 34 will set when:
e Signal is too low (kPa less than 14) and engine
running less than 1200 rpm.
OR
@ Engine running greater than 1200 rpm.
e Throttle position greater than 21% (over 1 5
volts).
2. If
the ECM recognizes the high hIAP signal, the
ECM and wiring are OK.
3. The "Scan" tool may not display 12 volts. The
important thing is that the ECM recognizes the
voltage as more than 4 volts, indicating that tho
ECM and CKT 432 are OK.
Diagnostic Aids:
An intermittent open in CKTs 432 or 416 will
result in a Code 34.
With the ignition "ON" and engine stopped, the
manifold pressure is equal to atmospheric pressure
and the signal voltage will be high. This information
is
used by the ECM as an indication of vehicle altitude
and is referred to as BARO. Comparison of this BARO
reading with a known good vehicle wilh the same
sensor is a good way to check accuracy of a "suspect"
sensor.
Iteading shoulci be the same, + .4 volts.
Refer to "Intermittnets" in Section "B".

CODE 43
ELECTRONIC SPARK CONTROL (ESC) CIRCUIT
5.0L (VIN E) "F" SERIES (TBI)
Circuit Description:
Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the
knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the
ECM to retard timing. The ECM will retard the timing when knock is detected and rpm is above about 900
rpm. Code 43 means the ECM has been low voltage at CKT 485 terminal
"B7" for longer than 5 seconds with the
engine running or the system has failed the functional check.
This system performs a functional check once per start up to check the ESC system. To perform this test the
ECM will advance the spark when coolant is above 95°C and at
a high load condition (near W.O.T.). The ECM
then checks the signal at
"B7" to see if a knock is detected. The functional check is performed once per start up
and if knock is detected when coolant is below 95°C (194°F) the test has passed and the functional check will not
be run. If the functional check fails, the "Service Engine Soon" light will
remain "ON" until ignition is turned
"OFF" or until a knock signal is detected.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. If the conditions for a Code 43 are present the
"Scan" will always display "yes". There should
not be a knock at idle unless an internal engine
problem, or a system problem exists.
2. This test will determine if the system is
functioning at this time. Usually a
knock signal
can be generated by tapping on the block close to
the area of the sensor.
3. Because Code 43 sets when the signal voltage on
CKT 485 remains low this test should cause the
signal on CKT 485 to go high. The
12 volts signal
should be seen by the ECM as "no knock"
it' the
ECM and wiring are OK.
4.
This test will determine if the knock signal is
being detected on CKT 496 or if the ESC module is
at fault. 5.
If
CKT 496 is routed to close to secondary ignition
wires the ESC
module may see the interference as
a knock signal.
6. This checks the ground circuit to the module. An
open ground will cause the voltage on CKT 485 to
be about
12 volts which would cause the Code 43
functional test to fail.
7. Contacting
CKT 496 with a test light to
12 volts
should generate a knock signal.
This will
determine if the ESC nodule is operating
correctly.
Diagnostic Aids:
Code 43 can be caused by a faulty connection at
the knock sensor at the ESC
lnodule or at the ECM.
Also check CKT 485 for possible open or short to
ground.
Iiefer to "Intcrmittents" in Section "B".

6EZ-A-50 5.0b (VIN E) DRIVEABILITY AND EMISSIONS
- GROUND -
CODE 45
OXYGEN SENSOR CIRCUIT
(RICH EXHAUST INDICAnEB)
5.OL (VlN E) ""FYESEBIES (TBI)
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
O2 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 45 is set when the O2 sensor signal voltage or
CKT
422.
@ Remains above .7 volts for 50 seconds; and in
"Closed Loop".
@ Engine time after start is 1 minute or more.
@ Throttle angle greater than 2% (about .2 volts
above idle voltage) but less than 25%.
Diagnostic Aids:
Using the "Scan", observe the block learn values at
different rpm conditions to determine when the
Code
45 may have been set. If the conditions for Code 45
exists, The block learn values will be around 115.
@ Fuel Pressure System will go rich if pressure is too
high. The ECM can compensate for some increase.
However, if it gets too high, a Code 45
may be set.
See "Fuel System Diagnosis", CHART
A-7.
Q See CHART A-7.
@ Check for fuel contaminated oil.
@ HE1 Shielding An open ground CKT 453 (ignition
system ref. low) may result in EMI, or induced
electrical "noise". The ECM looks
at this "noise" as
reference pulses. The additional pulses result in a
higher than actual engine speed signal. The ECM
then delivers too much fuel, causing system to go
rich. Engine tachometer will also show higher than
actual engine speed, which can help in diagnosing
this problem.
@ Canister Purge Check for fuel saturation. If full of
fuel, check canister control and hoses. See
"Canister Purge", Section
"(23".
@ MAP Sensor An output that causes the ECM to
sense a lower than normal
vacuum can cause the
system to go rich. Disconnecting the MAP sensor
will allow the ECM to set
a fixed value for the
sensor. Substitute a different MAP sensor if the the
rich condition is gone while the sensor is
disconnected.
r TPS An intermittent TPS output will cause the
system to go rich, due to
a false indication of the
engine accelerating.