sensor PONTIAC FIERO 1988 Service Repair Manual

6E3-A-24 5.OL (VIN F) & 5.71 (VIN 8) DRIVEABILITY AND EMISSIONS
OXYGEN ( 02) SENSOR
CODE 13
OXYGEN SENSOR CIRCUIT
(OPEN CIRCUIT)
5.OL (VIN F) & 5.7L (VIN 8) 'T" SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D7" and "D6". (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
.l0 volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below 360
" C(60OoF). 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 13
WILL SET:
@ Engine at normal operating temperature
(above 70°C)
@ At least 2 minutes engine time after start.
@ O2 signal voltage steady between .35 and .55
volts.
@ Throttle position sensor signal above 5%.
(about
.3 volts above closed throttle voltage).
@ All conditions must be met for about 60
seconds. If the conditions for
a Code 13 exist, the
system will not go "Closed Loop".
2. This will determine if the sensor is at fault or the
wiring or ECM is the cause of the Code 13.
3. For this test use only a high impedance digital
voltohm meter. This test checks the continuity of
CKTs 412 and 413. If CKT 413 is open, the ECM
voltage on CKT 412 will be over .6 volts (600 mV).
Diagnostic Aids:
Normal "Scan" voltage varies between 1OOmV to
999mV (.1 and 1.0 volt) while in "Closed Loop". Code
13 sets in one minute if voltage remains between .35
and .55 volts, but the system will go
"Open Loop" in
about
15 seconds.
Refer to "Intermittents" in Section
"B".

DRIVEABILITY AND EMISSIONS 5.0L (VIN F) €4 5.7L (VIN 8) 6E3-A-25
r RUN ENGINE ABOVE 1200 RPM FOR TWO MINUTES.
DOES "SCAN" INDICATE "CLOSED LOOP"?
JUMPER HARNESS
CKT412 TO GROUND.
00
mV) WITH ENGINE RUNNING.
SENSOR HARNESS CONNECTOR USING A DVM.
OVER
.6 VOLT LESS
THAN .3
FAULTY CONNECTION

6E3-A-26 5.OL (VIM F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
COOLANT SENSOR SIGNAL
-
CODE 14
COOLANT TEMPERATURE SENSOR CIRCUIT
(HIGH TEMPERATURE INDICATED)
5.OL (VIN F) & 5.7L (VIN 8) "F"" SERIES (PORT)
Circuit Description:
The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM
applies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high,
therefore, the ECM will see high signal voltage.
As the engine warms, the sensor resistance becomes less, and the voltage drops.
At normal engine operating
temperature
(85°C to 95"C), the voltage will measure about 1.5 to 2.0 volts.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 14 will set if:
@ signal voltage indicates a coolant temperature
above 130°C (266°F) for
3 seconds
2. This test will determine if CKT 410 is shorted to
ground which will cause the conditions for Code
14.
Diagnostic Aids:
Check harness routing for a potential short to
ground in
CKT 410.
"SCAN" tool displays engine temp, in degrees
centigrade. After engine is started, the temperature
should rise steadily to about
90°C, then stabilize when
thermostat opens.
Refer to "Intermittents" in Section
"B".

DRIVEABILITY AND EMISSIONS 5.0L (WIN F) & 5.7L (WIN 8) 6E3-A-27
DIAGNOSTIC AID
COOLANT SENSOR
TEMPERATURE TO RESISTANCE VALUES
(APPROXIMATE)
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

6E3-A-28 S.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
COOLANT SENSOR SIGNAL
CODE 15
COOLANT TEMPERATURE SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)
5.OL (VIN F) & 5.7L (VIN 8) 'Ti' SERIES (PORT)
Circuit Description:
The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM
applies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high,
therefore, the ECM will see high signal voltage.
As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating
temperature (85°C to
95'0, the voltage will measure about 1.5 to 2.0 volts at the ECM.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 15 will set if:
@ signal voltage indicates a coolant temperature
less than
-44" C (-47" F) for 3 seconds.
2. This test simulates a Code 14. If the ECM
recognizes the low signal voltage, (high temp.)
and
the "Scan" reads 130°C or above, the ECM and
wiring are OK.
3. This test will determine if CKT 410 is open. There
should be 5 volts present at sensor connector if
measured with
a DVM.
Diagnostic Aids:
A "SCAN" tool reads engine temperature in
degrees centigrade. After engine is started the
temperature should rise steadily
to about 90°C then
stabilize when thermostat opens.
A faulty connection, or an open in CKT 410 or 452
will result in a Code 15.
If Code 22 or 23 is also set, check CKT 452 for faulty
wiring or connections. Check terminals at sensor for
good contact. Refer to "Intermittents" in Section
"R".

DRIVEABILITY AND EMISSIONS 5.0L (VIN F) & 5.7L (VIN 8) 6E3-A-29
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
COOLANTTEMPERATURE SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED )
DIAGNOSTIC AID

6E3-A-30 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
FRONT VIEW TO MAT AND
OF CONNECTOR
COOLANT
452
ELK D2
416 GRY - C14
CODE 21
THROmLE POSITION SENSOR (TPS) CIRCUIT
(SIGNAL VOLTAGE HIGH)
5.OL (VIN I") & 5.7L (VIN 8) 'T" 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:
@ TPS signal voltage is greater than 2.5 volts
@ Engine is running
@ Air flow is less than 12 GMIsec.
e All conditions met for 3 seconds.
OR
@ TPS signal voltage over about 4.8 volts with
ignition "ON".
With throttle closed, the TPS should read less
than .62 volts. If it doesn't check adjustment.
2. With the TPS sensor disconnected, the TPS
voltage should go low if the ECM and wiring is
OK.
Diagnostic Aids:
A "SCAN" tool reads throttle position in volts.
Should read
.54V f .08V with throttle closed and
ignition "ON" or at idle. 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".
3. Probing CKT 452 with a test light checks the 5V
return CKT, because
a faulty 5V return will cause
a Code 21.

6E3-A-32 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
FRONT VIEW TO MAT AND OF CONNECTOR COOLANT
SENSORS
452 BLK - D2 .
416 GUY - C14
CODE 22
THROTLE POSITION SENSOR (WS) CIRCUIT
(SIGNAL VOLTAGE LOW)
5.OL (VIN F) & 5.7L (VIN 8) "F'YSERIES (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. Code22willsetiE
@ Engine running
TPS signal voltage is less than about
.% volt for
3 seconds.
2. Simulates
Code
21: (high voltage) If the ECM
recognizes the high signal voltage the ECM and
wiring are
OK.
3. TPS adjustment: With throttle closed, the TPS
voltage reading should be
54V f .08V.
4. This simulates a high signal voltage to check for
an open in CKT
417.
Diagnostic Aids:
A "Scan" tool reads throttle position in volts.
Should read
54V + .08V with throttle closed and
ignition
"ON" or at idle. Voltage should increase at a
steady rate as throttle is moved toward WOT.
An open or short to ground in
CKTs 416 or 417
will result in a Code 22.
Refer to "Intermittents" in Section
"B".

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-A-33
(SIGNAL VOLTAGE LOW)
JUMPER CKTS 416 & 417 TOGETHER.
"SCAN" SHOULD DISPLAY TPS OVER
4.0 V (4000 mV
"SCAN" TOOL SHOULD DISPLAY TPS OVER
SHORTED TO GROUND
FAULTY CONNECTION. ORTED
TO SENSOR GROUND CIRCUIT.
FAULTY ECM CONNECTION.

6E3-A-34 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
MANIFOLD AIR
TEMPERATURE
MAT SENSOR SIGNAL
NSOR GROUND
COOLANT
TEMPERATURE
SENSOR
CODE 23
MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)
5.OL (VIN F) & 5.7L (VIN 8) "F" SERIES (PORT)
Circuit Description:
'I'he MAT sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6
volts) on CKT 472 to the sensor. When the air is cold, the sensor (thermistor) resistance is high, therefore, the
ECY will see a high signal voltage. If the air is warm, the sensor resistance is low, therefore, the ECM will see
a low voltage.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 23 will set if:
@ A signal voltage indicates u manifold air
temperature below -30°C (-22°F) for
12
seconds.
@ Time since engine start is 1 minute or longer.
@ No VSS (vehicle not moving)
2. A Code 23 will set, due to an open sensor, wire, or
connection. This test will determine if the wiring
and ECM are OK. The MAT sensor is difficult to
reach and this test can be performed
by
disconnecting the MAT jumper harness connector.
If the "Scan" indicates a temperature of over
130°C the jumper harness to the sensor should be
checked before replacing the sensor.
3. This will determine if the signal CKT 472 or the
5V return CKT 452 is open.
Diagnostic Aids:
A "SCAN" tool reads temperature of the air
entering the engine and should read close to ambient
air temperature when engine is cold, and rises as
underhood temperature increases.
Carefully check harness
ancl connections for
possible open CKT
472 or 452.
Refer to "Intermittents" in Section
"H".