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

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

Engine is running.

DTC P0117 diagnostic runs continuously once the above conditions have been met.

P0117 is a (type B) DTC.

To locate an intermittent problem, use Scan tool to monitor ECT temperature with ignition On, engine Off. Wiggling wires while watching for a change in ECT 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 gauge will display COLD if DTC P0117 is active.

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

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

ECT sensor reading may be compared to IAT sensor reading on Scan tool after the vehicle has been sitting longer than 6 hours with the ignition Off. Both readings should be within 6°C or 10°F of each other.