Engine Coolant Temperature Sensor: Operation

The PCM determines engine coolant temperature from the engine coolant temperature (ECT) sensor. The ECT sensor is a two wire Negative Temperature Coefficient (NTC) sensor. As temperature increases, resistance in the sensor decreases. The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As coolant temperature varies, the coolant temperature sensor resistance changes resulting in a different voltage value at the PCM engine coolant sense circuit.

Until the engine reaches operating temperature, the PCM demands slightly richer air-fuel mixtures and higher idle speeds.

This sensor is also used for cooling fan control, A/C cutoff at high coolant temperatures, and temperature gauge operation.