P0128

Test 1:

Test 2 - Test 4:

Test 5 - Test 7:

Test 8 - Test 11:

Test 12 - Test 13:

SYMPTOM
P0128-THERMOSTAT RATIONALITY

WHEN MONITORED
The engine running. During cold start.

SET CONDITION
The PCM predicts a coolant temperature value that it will compare to the actual coolant temperature. If the two coolant temperature values are not within 10° C (50° F) of each other an error is detected. Two Trip Fault.

POSSIBLE CAUSES
- Good trip equal to zero
- Low coolant level
- Other possible causes
- Signal circuit shorted to battery voltage
- Monitor engine coolant temperature
- Temperature sensor voltage below 1.0 volt
- Signal circuit open
- Sensor ground circuit open
- Signal circuit shorted to ground
- Signal circuit shorted to sensor ground
- PCM low
- PCM high