The ECT sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and increases as the coolant temperature decreases. This provides a reference signal to the ECM, which indicates engine coolant temperature. The signal sent to the ECM by the ECT sensor helps the ECM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT is a two wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature.