P0128-THERMOSTAT RATIONALITY

For a complete wiring diagram Refer to Section 8W.


  • 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.


Possible Causes
  
TEMPERATURE SENSOR WIRING OR CONNECTORS
  
ENGINE COOLANT LEVEL AND CONDITION
  
THERMOSTAT
  
TEMPERATURE SENSOR
  

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - STANDARD PROCEDURE).



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.




Were any problems found?

Yes


No
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2.CHECKING THE ENGINE COOLANT TEMPERATURE SENSOR OPERATION.



Were any problems found?

Yes


No