Theory Of Operation

The Engine Coolant Temperature (ECT) Sensor is a variable resistor that functions as a normal two wire, 5-Volt sensor. The Powertrain Control Module (PCM) supplies the ECT Sensor with a 5-Volt reference and a filtered ground (return) circuit. For the ECT Sensor diagnostic, the PCM internally monitors the voltage on the signal circuit, which is converted into a temperature reading. If the voltage reads above the high calibrated threshold, or below the low calibrated threshold, a circuit high or low fault is set.