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

Engine Coolant Temperature Sensor:

PURPOSE
The Engine Control Module (ECM) decides whether the engine is "cold" based on this sensor input and controls the fuel injection rate and fast idle speed accordingly.

OPERATION
The engine coolant temperature sensor is a negative temperature coefficient thermistor. It converts engine coolant temperature into a voltage for the ECM to read.

The ECM supplies a 5 volt reference and a ground for the sensor.
- When coolant temperature increases sensor output voltage decreases.
- When coolant temperature decreases sensor output voltage increases.

CONSTRUCTION
The Coolant Temperature Sensor is a thermistor type sensor.