Engine Coolant Temperature Sensor
Engine Coolant Temperature (ECT) sensor monitors engine coolant temperature. The temperature sensor is mounted into the engine near the thermostat. See Fig 1 or Fig 2 . Engine control module/powertrain control module uses ECT sensor information to adjust air/fuel mixture, idle speed and signal radiator fan controller as necessary.
The engine coolant temperature sensor is a negative temperature coefficient type of resistor. It has the characteristic that when the engine coolant temperature rises the resistor decreases. The engine coolant temperature sensor output voltage increases when the resistor increases and decreases when the resistor decreases.