Coolant Temperature

The scan tool range is -39° C to +140° C (-38° F to +284° F). The PCM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor that changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the PCM monitors a high signal voltage and interprets the voltage as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.