Engine Coolant Temperature Sensor

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Suburban, 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 the engine coolant. ECT sensor is located on side of left cylinder head. The PCM supplies 5 volts to the signal circuit and a ground for the ECT low reference circuit. When ECT is low, sensor resistance is high. When ECT is high, sensor resistance is low. The PCM uses this input for engine controls and enabling criteria for diagnostics. The internal clock of the PCM will record the amount of time ignition is off. At restart, PCM will compare the temperature difference between the ECT and the IAT sensor. Before failing this test, the PCM will perform a calculation to determine the presence of a block heater. If PCM detects that the temperature difference is not within the calibrated amount after the ignition off time, a DTC will set. To diagnose, see SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.