Coolant Temperature Sensor

The engine coolant temperature sensor (CTS) is used to measure the temperature of the engine coolant of an engine. The readings from this sensor are then fed back to the engine control unit (ECU), which uses this data to adjust the fuel injection and ignition timing.
Common signs of a bad or failing coolant temperature sensor include poor fuel economy, engine overheating black smoke from the engine, and the Check Engine Light turning on.