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

Engine Coolant Temperature (ECT) Sensor:

DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) which is mounted in the engine coolant stream. Low coolant temperature produces a high resistance, 100,000 ohms at 40° C (-40° F) and high coolant temperature produces low resistance, 70 ohms at 30° 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.