P0128

Test 1:

Test 2 - 4:

Test 5 - 7:

Test 8 - 11:

Test 12 - 13:

SYMPTOM
P0128-THERMOSTAT RATIONALITY

WHEN MONITORED
The engine running.

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 (18 °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
- Thermostat Operation
- 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