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

ECT Sensor:

ECT Sensor Cross Section:

Engine Coolant Temperature Sensor

The sensor outputs a voltage to the ECM which decreases as temperature increases.

Operation

The Engine Coolant Temperature Sensor (ECT) is located in the thermostat housing and reacts to engine outlet coolant temperature changes, providing an input to the ECM. The sensor has a negative temperature coefficient so that the sensor resistance decreases as temperature rises.

The thermostat housing mounted ECT sensor reacts to engine outlet coolant temperature changes and inputs the ECM.

Monitoring Procedure
Following engine start-up, the ECT sensor output is monitored to check for coolant temperature rise. After a period, which is determined by the start up temperature, the sensor is expected to indicate greater than 70°C. If the indicated temperature is less than 70°C the range/performance failure judgement is made. The same judgement is made should a temperature drop of more than 20°C in 2 seconds be recorded. The DTC is stored if the failure judgement is made on two successive trips.

Sensor output is continuously monitored for high and low out of range values. If a sustained high, or low input to the ECM is seen (indicating a harness or connector fault), a high/low failure judgement is made. The relevant DTC is stored if the failure judgement is made on two successive trips.





Temperature/Resistance Relationship Graph