Circuit/System Verification
CAUTION:
Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.
IMPORTANT:
A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.
- Verify the proper heat range and for a stuck open thermostat. Refer to Thermostat Diagnosis .
- Inspect the ECT sensor terminals for corrosion and for engine coolant leaking through the sensor.
- Verify the proper operation of the engine cooling fan, fan stuck ON/fully engaged all the time.
- Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Draining and Filling Cooling System (Static Fill) or Draining and Filling Cooling System (Vac N Fill) .
- Engine running, observe the DTC information with a scan tool. DTC P0128 should not set.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame Records data.