Engine Temperature Sensor: Description and Operation

Engine Coolant Temperature Sensor:

The coolant temperature sensor is a thermistor (a device whose resistance changes with temperature) mounted in the engine cooling system. Low temperature produces high resistance (100K ohms at -40°C / -40°F) while high temperature produces low resistance (70 ohms at 130°C / 266°F).

The ECM supplies a 5V signal to the sensor and measures voltage variation. By measuring this variation, the ECM measures coolant temperature. This input is a factor in calculations involving most ECM controlled systems.