Engine Coolant Temperature Sensor
An engine coolant temperature sensor ECT is a variable resister sensor. This just means that the sensors signal changes or varies according to the temperature of it's environment. This sensor is vital in maintaining an engines proper operating temperature. It's located in the coolant stream usually on or around the thermostat housing. It is constantly sensing the temperature of the engines coolant.
In the old days it was a switch, either on or off. Now they send a varying or changing voltage signal to the PCM in relation to the engines temperature. It is a NTC or negative temperature coefficient thermistor meaning that as the temperature increases the resistance decreases. Another way of saying this is more voltage is dropped across this sensor when its cold than when its hot. The PCM uses these voltage signals to make adjustments to both engine (Fuel Injectors) and transmission (Torque Converter Clutch) actuators. Coolant temperature sensor symptoms would include the vehicle running rich and the inability or delay in TCC engagement.
Testing of this sensor is done with either an ohmmeter or voltage meter. With an ohmmeter test the resistance between the two terminals at certain temperatures and compare to manufacturers specifications. This sensor can be heated in or cooled in water and then compared to manufacturers resistance specifications as well. Use a voltage meter to measure the voltage readings, notice that less voltage will be dropped across the sensor as the engine warms up.
