Low engine coolant level
Faulty Engine Coolant Thermostat
Faulty Engine Coolant Temperature (ECT) sensor
Engine Coolant Temperature sensor harness is open or shorted
Engine Coolant Temperature sensor circuit poor electrical connection
Engine Light ON (or Service Engine Soon Warning Light)
The Engine Coolant Temperature (ECT) sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal from the Engine Control Module (ECM). The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor that is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases. The Diagnostic Trouble Code (DTC) will be set when an excessively low voltage from the sensor is sent to ECM.