Pontiac Fiero 1988 Service Manual page 613

6E3-A-30 DRIVABILITY AND EMISSIONS - FUEL INJECTION (PORT)
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EZJ
COOLANT
TEMPERATURE
SENSOR
ECM
I »
T
• 410 Y E L
452 BLK
C10
D12
452
TO TPS
COOLANT SENSOR
SIGNAL
5V
5-19-87
5-8-87
* 5 S 1 3 7 5 - 6 E
C O D E 15
COOLANT TEMPERATURE SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)
2.8L "P" 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 ( 8 5 ° C to 9 5 ° C ) 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:
• Ignition "ON" engine not running
• Coolant temperature less than - 3 0 ° C (-22°F),
for 3 seconds
• No Code 23
• MAT temperature indicated above - 2 5 ° C
(-13°F)
or
• Engine running longer than 1 min
• Signal voltage indicates a coolant temp, less
than - 3 0 ° C (-22°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 1 3 0 ° C or above, the ECM and
wiring are OK.
3. This test will determine ifCKT 410 is open. There
should be 5 volts present at sensor connector if
measured with a DVOM.
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.
If Code 21 is also set, check CKT 452 for faulty
wiring or connections. Check terminals at sensor for
good contact.
Refer to Intermittents in Section "B".