Coolant Temperature Sensor (CTS):
The engine coolant temperature 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 computer sends a 5.0 volt signal to the coolant temperature sensor through a resistor in the ECM and measures the voltage. The voltage will be high or low depending on coolant temperature. By varying the voltage, the computer will sense engine coolant temperature.