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

Engine Coolant Temperature (ECT) Sensor
The ECT sensor (1) is located in the engine block below the engine coolant temperature sending unit (2). The ECT sensor is a thermistor (a variable resistor that changes value when the temperature changes). The ECT sensor is connected in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage drop across the ECT sensor and converts the voltage reading into a temperature value. The ECT sensor voltage reading at the PCM will vary with the changes in the engine temperature.