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

Engine Coolant Temperature Sensor:

The Engine Coolant Temperature (ECT) sensor is threaded into a coolant passage with the sensing bulb extending into the coolant.
The ECT sensor is a negative temperature coefficient sensor, meaning that as the temperature of the sensor increases, the resistance will decrease. As the resistance value changes, the signal sensed by the Electronic Control Assembly (ECA) also changes. The ECA reads the varying sensor resistance and determines the engine operating temperature, using this information to optimize the air/fuel mixture and ignition timing.
The ECT sensor will also set a fault code when the ECA determines the output signal to be out of the normal operating range.

ECT resistances:

-40° 269 K ohms

32° 95 K ohms

77° 29 K ohms

248° 1.2 K ohms