Engine Coolant Temperature Sensor
WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of engine coolant. ECT sensor is located on side of left cylinder head. See Fig 1 . 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 - 4.3L SIERRA & SILVERADO article.