For 1990-2009 cars

The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The powertrain control module (PCM) monitors the ECT to determine the engine coolant temperature. As the coolant temperature rises, the resistance of the ECT varies. If the coolant temperature exceeds an acceptable level, the PCM detects this change and sends a class 2 message to the instrument panel cluster (IPC). The IPC then illuminates the HOT COOLANT TEMP message.