Engine Coolant Temperature Sensor: Operation
WARNING: This page is about a different car, the 2006 Dodge Viper. However, it is still accessible from the selected car via links, so may be relevant.
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.