P0128

P0128-THERMOSTAT RATIONALITY

For a complete wiring diagram refer to Diagrams/Electrical.

- When Monitored:

With the engine running, start up coolant temperature between -8° C (17.6° F) and 50° C (122° F), the difference between ambient temperature and coolant temperature less than 10° C (50° F) and average vehicle speed greater than 16 kph (10 mph) for more than 18% of vehicle run time.

- Set Condition:

The PCM detects that the actual engine coolant temperature does not reach the predicted engine coolant temperature within a specific time. Two trip fault. Three good trips to turn off the MIL.






Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test

1. CHECKING THE TEMPERATURE SENSORS.

NOTE: Diagnose and repair any ambient air temperature (AAT), intake air temperature (IAT), or engine coolant temperature (ECT) sensor circuit or rationality DTCs before continuing with this test.

NOTE: Diagnose and repair any crankshaft (CKP) or camshaft (CMP) sensor circuit or rationality DTCs before continuing with this test.

NOTE: Diagnose and repair any communication DTCs before continuing with this test.

NOTE: Verify that the Pinion Factor has been programmed correctly into the PCM.

Perform the diagnostic procedure for *CHECKING THE TEMPERATURE SENSORS. Checking the Temperature Sensors

Were any problems found?

Yes

- Repair as necessary.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Go to 2

2. CHECKING THE ENGINE COOLANT TEMPERATURE SENSOR OPERATION.

Perform the diagnostic procedure for *CHECKING THE ENGINE COOLANT TEMPERATURE SENSOR OPERATION. Checking the Engine Coolant Temperature Sensor Operation

Were any problems found?

Yes

- Repair as necessary.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure. Checking for an Intermittent DTC