Possible Causes

ECM illuminates MIL and sets DTC P0125 when voltage sent to ECM from ECT sensor is not practical, even when some time has passed since starting engine. Or, engine coolant temperature is insufficient for closed loop fuel control. Possible causes are:

• ECT sensor circuit open or shorted.
• Poor, loose, corroded or damaged terminal connections.
• Defective ECT sensor.
• Defective thermostat.