ECT Sensor

The scan tool displays -40°C to +151°C (-40°F to +304 °F). The ECT sensor is mounted in the coolant stream. The PCM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. If the sensor's internal resistance is high, the PCM monitors the signal voltage, and interprets the high voltage as a cold engine. As the sensor's internal resistance decreases, the voltage signal decreases, and the PCM interprets the lower voltage as a warm engine.