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

Engine Coolant Temperature Sensor:

PURPOSE
The engine Coolant Temperature Sensor (CTS) provides engine temperature information to the control. The control unit uses this information to determine open-loop/closed loop operation, and make temperature related adjustments to the fuel, ignition and emission control systems.

OPERATION
The Sensor is a thermistor, installed where it protrudes into the engine coolant flow. Its resistance varies with changing temperature. At low temperatures its resistance is high. At high temperatures, its resistance is low. The ECM/PCM sends a 5.0 volt reference signal to sensor through a resistor in the computer, and then monitors the voltage in the circuit. The measured voltage varies with changes in coolant temperature, due to the changing resistance of the sensor. Each measured voltage value corresponds to a specific coolant temperature. By monitoring the circuit voltage, the computer can calculate the engine temperature and make necessary adjustments.