The coolant temperature sensor is a component of the engine cooling system. Mounted inside your engine, the device relies on electrical resistance to measure engine temperatures.
Your engine produces a good deal of heat as a byproduct of combustion. Some of that heat is necessary for proper engine function. But too much heat can cause damage. Therefore, liquid coolant (also known as “antifreeze”) is circulated through the engine where it absorbs some of the heat. The coolant flows from the engine to the radiator, where heat dissipates into the atmosphere before traveling back to the engine to pick up more heat.
In order for the cooling system to do its job properly (and for your engine to work as it should), it is essential that the temperature of your engine be monitored constantly. That is the responsibility of the coolant temperature sensor. Mounted inside the engine, the device uses electrical resistance to measure the temperature of the coolant. The information is sent to the engine control module (the ECM) so that the computer can make adjustments to things like engine timing and fuel injector function. The sensor also informs the temperature gauge or engine temperature light on the dashboard.