Engine Temperature Sensor: Description and Operation

Coolant Temperature Sensor:

The Coolant Temperature Sensor is a thermistor which relays an engine coolant temperature signal to the ECM. Temperature changes cause resistance through the sensor to vary, thus creating a signal the ECM can interpret. This signal is used as one of the criteria to determine when the system is ready to enter closed loop mode. The information is also used to modify the open loop duty cycle.

At 20°C (68°F), resistance of the sensor is between 2 - 3K ohms. When the engine is warm (80°C / 176°F), resistance falls to between 200 - 400 ohms.