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

DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor (a variable resistor that changes along with temperature changes) in series with a fixed resistor in the Powertrain Control Module (PCM) that measures the temperature of the engine coolant.

OPERATION
The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts it into a temperature reading. When the engine is cold the ECT sensor resistance is high, and when the engine temperature is warm the ECT sensor resistance is low. Therefore, when the engine is cold the PCM will receive a high voltage input, and when the engine is warm, the PCM will receive a low voltage input.