The engine coolant temperature (ECT) sensor is a thermistor that varies resistance according to changes in the engine coolant temperature. The ECM supplies a 5-volt reference through a pull-up resistor to the sensor, which is connected to a ground. When the sensor is cold it has high resistance (high signal voltage at ECM). As the sensor temperature increases, its resistance decreases (lower signal voltage at ECM). The ECM uses the signal voltage to determine engine coolant temperature. DTC P0117 sets when the ECT sensor signal voltage at the ECM is below the calibrated voltage value (over the calibrated temperature value).

DTC P0117 will set if the ECT sensor temperature is over 140°C (284°F) when:

DTC P0117 diagnostic runs continuously with the engine cranking/running.

P0117 is a type B DTC.

To locate an intermittent problem, use the scan tool to monitor the ECT sensor temperature with the ignition On and the engine Off. Wiggling the wires while watching for a change in the ECT sensor temperature may locate the area where a short to ground may exist.

Engine coolant leaking from the sensor into the sensor connector will cause a shorted condition across the sensor terminals resulting in an elevated temperature.

The Coolant Temperature gage will display COLD if DTC P0117 is active.

The ECM will command the cooling fans On if DTC P0117 is active.

Refer to the ECT General Description for the Temperature vs. Resistance chart.