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

Engine Coolant Temperature (ECT) Sensor:

PURPOSE
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperature produces a high resistance (100,000 ohms at -40° C (-40° F) while high temperature causes low resistance (70 ohms at 130° C (266° F).

OPERATION
The control module supplies a 5 volt signal to the ECT sensor 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.