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

ECT Circuit (Typical):

Engine Coolant Temperature Sensor:

PURPOSE
The Engine Coolant Temperature (ECT) sensor allows the control module to monitor temperature of engine coolant. Engine coolant temperature affects the cold advance, glow plug systems and electronic transmission operation.


Operation
The ECT sensor is a thermistor that is located in the engine coolant flow. Low coolant temperature sensor produces a high resistance (100,000 ohms at -40°C/-40°F). High coolant temperature, produces a low resistance (70 ohms at 130°C/266°F).

The control module sends a 5.0 volt signal to the ECT through a resistor in the control module and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot. Engine coolant temperature affects most systems controlled by the control module