Engine Coolant Temperature Sensor
An engine coolant temperature sensor or ECT sensor is a variable resister that uses resistance to change a 5 volt reference signal from the PCM. The sensor's signal changes according to the engine's coolant temperature. It’s a vital component for maintaining an engine’s normal operating temperature. Located in the coolant stream, usually on or around the thermostat housing, its job is to constantly sense the temperature of the engine’s coolant.
There was a time when this type of sensor was either switched on or off. Now it’s a resistor that sends a varying or changing voltage signal to the PCM in relation to the engine’s coolant temperature. They are NTC or negative temperature coefficient thermistors. As the coolant’s temperature increases, the sensor’s resistance decreases. More voltage is dropped across this sensor when it’s cold than when it’s hot.
The PCM uses this voltage signal to make adjustments to both engine (fans, fuel injectors) and transmission (torque converter clutch) actuators. The symptoms of a faulty ECT sensor include a rich air fuel mixture, poor fuel mileage and an inoperative torque converter clutch.