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

ENGINE COOLANT TEMPERATURE SENSOR

The Engine Coolant Temperature (ECT) Sensor supplies an engine coolant temperature signal to the ECM, which uses the signal in controlling the:

^ Injection period
^ Idling speed
^ Engine cooling fan operation
^ Ignition timing
^ Diagnostic functions

The sensor incorporates a temperature-sensitive resistance with a Negative Temperature Coefficient (NTC). The ECM delivers a nominal (unloaded) output of 5 Volts, across an internal resistance, to one of the sensor terminals. The second terminal is grounded.

The voltage across the sensor is a function of the engine temperature and, therefore, of the sensor resistance. The value, which may vary from 0 Volts to 5 Volts, is high when the engine is cold and low when the engine is hot. To increase the accuracy of the signal at high temperatures (above 60°C / 140°F), the ECM switches internally to a smaller resistance at one-second intervals. The signal increases by approx. 0.5 Volts when this occurs.

The ECM will adopt a substitute value if the ECT sensor signal is lost or becomes faulty.

The sensor is mounted on the thermostat housing.