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. The ECT is grounded by the PCM through circuit 469. As the coolant temperature rises, the resistance of the ECT varies. If the coolant temperature exceeds an acceptable level, the PCM detects this change at circuit 410 and sends a class 2 message through the serial data line to the instrument panel cluster (IPC). The IPC then illuminates the HOT COOLANT TEMP message.