With Powertrain Control Module - PCM

Engine Coolant Temperature (ECT) Sensor Circuit:

Purpose:
The Engine Coolant Temperature (ECT) sensor is a thermistor that is located in the engine coolant flow. When the coolant temperature is low, the sensor produces a high resistance. When the coolant temperature is high, the sensor produces a low resistance.

The control module sends a 5 volt signal to the ECT through a resistor in the computer and measures the voltage. The voltage will be high or low depending on coolant temperature. By varying the voltage the computer can determine engine coolant temperature.