P0128

P0128 - Thermostat Rationality






For wiring diagrams, refer to.

• 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. Refer to => Non-DTC Based Diagnostics. Pre-Diagnostic Troubleshooting Procedure

Test Step 1 - Checking the Temperature Sensors.

• Diagnose and repair any ambient air temperature , intake air temperature , or engine coolant temperature sensor circuit or rationality DTCs before continuing with this test.

• Diagnose and repair any crankshaft or camshaft sensor circuit or rationality DTCs before continuing with this test.

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

• Verify that the pinion factor has been programmed correctly into the PCM.

• Perform the diagnostic procedure for checking the temperature sensors. Refer to => Non-DTC Based Diagnostics.

Were any problems found?

Yes

• Repair as necessary.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Go to Test Step 2 => [ Test
Step 2 - Checking the Engine Coolant Temperature Sensor Operation. ]

Test Step 2 - Checking the Engine Coolant Temperature Sensor Operation.

• Perform the diagnostic procedure for Checking the Engine Coolant Temperature Sensor Operation. Refer to => Non-DTC Based Diagnostics. Engine Coolant Temperature Sensor Operation Test

Were any problems found?

Yes

• Repair as necessary.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Refer to the checking for an intermittent DTC diagnostic procedure. Refer to => Non-DTC Based Diagnostics. Checking for an Intermittent DTC