What Is a Coolant Temperature Sensor?

A coolant temperature sensor (ECT) is the variable resistant thermistor in the vehicle’s engine that changes resistance as the coolant temperature changes as well. The information received from the coolant temperature sensor by the on-board engine computer is used to regulate the emissions and fuel control functions as well as the ignition system.

The data received from this sensor is also used to determine whether the radiator cooling fan in the engine needs to turn on or off. Often called the “master” sensor, the coolant temperature sensor essentially tells if the vehicle’s engine is warming up, too cold, overheating or is running at a normal temperature.

Common Type of Coolant Temperature Sensor

Most coolant sensors used for new cars are thermistors and these vehicles often use the Negative Temperature Coefficient (NTC) type. The Negative Temperature Coefficient is the type of coolant sensor wherein the resistance drops as the temperature in the engine of the car goes up. The internal resistance of this type of sensor is high when the engine of the car is cold. On the other hand, the resistance of the coolant sensor goes down until the sensor reaches up to the minimum value.

However, a different type of coolant temperature sensor is sometimes used for older cars. These old model cars often have a switch for a temperature sensor where the driver just turns the switch on and off.

On the other hand, there are some vehicles that have two coolant sensors. These vehicles have a coolant temperature sending unit and a coolant temperature sensor. The sending unit manipulates the temperature gauge while the sensor sends the signal to the on-board computer.

Uses of Coolant Temperature Sensor

There are several uses of a coolant temperature sensor. Aside from the fact that the information received from the coolant sensor is used to determine the temperature of the engine, the data is also used for fuel enrichment on fuel injected engines. If the coolant sensor detects that the engine is too cold, the Powertrain Control Module (PCM) relays this information to the on-board computer which in turn increases the injector pulse width.

The information is also used to regulate the temperature of the engine. If the engine becomes too hot the cooling is turned on. If the engine becomes too cold, the coolant sensor sends a signal to the computer and the cooling fan is turned off.

The coolant temperature sensor is also used for spark advance and retard. The computer limits the spark advance until the temperature sensor provides the information that the engine has reached the normal operating temperature needed.

Finding the Coolant Temperature Sensor

Finding the coolant temperature sensor is quite easy to do. The sensor is often located near or around the thermostat housing where the intake manifold is situated. However, there are some vehicles that have the coolant temperature sensor by the cylinder head.

For the coolant temperature sensor to work properly, it is placed in such a way that the tip is in direct contact with the coolant of the vehicle’s engine.