Pontiac Fiero 1988 Service Manual page 611

6E3-A-28 DRIVABILITY AND EMISSIONS - FUEL INJECTION (PORT)
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COOLANT
TEMPERATURE
SENSOR
ECM
• 410 YEL
452 BLK
C10
D12
TO TPS
COOLANT SENSOR
SIGNAL
5V
5-19-87
5-8-87
* 5 S 1 3 7 5 - 6 E
C O D E 1 4
COOLANT TEMPERATURE SENSOR CIRCUIT
( H I G H T E M P E R A T U R E I N D I C A T E D )
2.8L "P" SERIES
(PORT)
Circuit
D e s c r i p t i o n :
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.
Test
D e s c r i p t i o n :
Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 14 will set if:
• Signal voltage indicates a coolant
temperature above 1 3 5 ° C (275°F) for 3 seconds
® Engine running longer than 20 seconds
2. This test will determine if CKT 410 is shorted to
ground which will cause the conditions for Code
14.
D i a g n o s t i c A i d s :
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 9 0 ° C then stabilize when
thermostat opens.
Refer to "Intermittents" in Section "B".