Circuit/System Description
WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. 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 the engine coolant. The control module supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the control module detects a high voltage on the ECT signal circuit. With lower sensor resistance, the control module detects a lower voltage on the ECT signal circuit.