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Codes: P0128 Problem: Faulty thermostat Test & Fix: The default of a trouble code P0128 is to run the cooing fans and make the temperature gauge inoperative. This code indicates the engine did not warm up as fast as it should have. Check for the thermostat to be stuck open. Replace the thermostat and retest. Monitor the engine temperature. It should reach 195 degrees F within a few minutes. Tests/Procedures:
1. Review the engine temperature through the scan tool to reach a warm engine in a reasonable amount of time.
2. Verify good coolant level and condition.
3. Replace the thermostat.
Cooling SystemThermostat Tips: This code shows that the engine has not reached a predetermined temperature based on engine run time and airflow entering the engine. A stuck thermostat will cause this code. The temperature gauge may be inoperative with this code set.
P0128 Engine Coolant Temperature Below Thermostat Regulating Temperature - With Automatic Transmission
Check the operation of the thermostat (it may be stuck open) Coolant level is too low and the coolant mixture is incorrectECT sensor connector is damaged (inspect pins for damage and for moisture)ECT sensor signal circuit has a high resistance conditionECT sensor has failed