Engine Coolant Temperature Sensor

The Engine Coolant Temperature (ECT) sensor threads into the coolant system. See Figure or Figure . The ECT sensor provides an input to the PCM. As coolant temperature varies, the ECT sensor resistance changes resulting in a different input voltage to the PCM. When the engine is cold, the PCM will demand slightly richer air/fuel mixtures and higher idle speeds until normal operating temperatures are reached. The ECT sensor input also determines operation of the low and high speed fans.