Scan Tool Data Definitions - PCM

ECT Sensor: The scan tool displays a range of 39 to +140°C (38 to +284°F). The powertrain control module (PCM) applies 5.0 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as the engine temperature changes. When the sensor is cold, internal resistance is high, the PCM senses 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.