The Engine Coolant Temperature (ECT) sensor resistance changes in response to the engine coolant temperature. The sensor resistance decreases as the coolant temperature increases. This provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. A 5 volt reference signal is sent to the sensor and the signal return is based upon the change in the sensor resistance due to temperature.