Engine Coolant Temperature Sensor

The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of engine coolant. ECT is located on top front of cylinder head, near PCM. See Figure . The PCM supplies 5 volts to the ECT signal circuit and ground for the ECT low reference circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance decreases. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on the ECT signal circuit. If PCM detects an out-of-range signal voltage, a DTC will set. To diagnose, see SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.