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

Fig 15 Engine Coolant Temperature Sensor:

ENGINE COOLANT TEMPERATURE SENSOR
The engine coolant temperature sensor threads into the water jacket next to thermostat housing. The sensor provides an input to the powertrain control module (PCM). As coolant temperature varies, the sensor resistance changes, resulting in a different input voltage to the PCM.

The PCM contains different spark advance schedules for cold and warm engine operation. The schedules reduce engine emission and improve driveability. When the engine is cold, the PCM will demand slightly richer air-fuel mixtures and higher idle speeds until normal operating temperatures are reached.

The engine coolant sensor input also determines operation of the low and high speed cooling fans.