Engine Coolant Temperature Sensor

The engine coolant temperature sensor provides the PCM with the temperature of the engine coolant. A 5-volt reference signal is sent from the PCM to the engine coolant temperature sensor over the ECT sensor signal circuit. A variable resistor inside the sensor varies the voltage. That varied voltage provides a signal back to the PCM. Remaining voltage from the engine coolant temperature sensor is sent back to the PCM through the low reference circuit.