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

The engine temperature sensor, located on top of thermostat housing on Q45 models; top of the water inlet housing on M30 models; and behind the oil filter on G20 models, detects engine coolant temperature and transmits a signal to the ECU. The temperature sensing unit employs a thermistor which is sensitive to the change in temperature. Electrical resistance of the thermistor decreases in response to temperature rise.