Coolant Temperature Sensor/Switch (For Computer): Description and Operation

Engine Coolant Temperature Sensor:

Engine Coolant Temperature (ECT) Sensor Circuit Diagram:

DESCRIPTION
The engine Coolant Temperature Sensor (CTS) is a thermistor installed so it protrudes into 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.

OPERATION
The ECM applies a 5V reference voltage to the sensor, through a resistor in the ECM, and then monitors the voltage in the circuit. When the engine is cold, resistance through the sensor will be high and the voltage in the circuit will be near the reference voltage of 5V. When the temperature increases, resistance drops, more current flows through the circuit and the voltage in the circuit will drop. Each voltage value corresponds to a specific resistance through the sensor and a specific engine temperature. The ECM measures this voltage and calculates the engine coolant temperature.