DTC P0128: Coolant Thermostat Inoperative: Condition

DTC is set when Engine Control Module (ECM) detects engine coolant temperature is lower than 167F (75C), after vehicle has been driven under specified conditions. MIL is illuminated when ECM detects malfunction during 2 consecutive drive cycles. Possible causes are:

• ECM malfunction.
• Engine Coolant Temperature (ECT) sensor malfunction.
• ECT sensor circuit malfunction.
• Thermostat malfunction.