Located in the engine coolant passage of the cylinder head, the Engine Coolant Temperature Sensor (ECTS) is used for detecting the engine coolant temperature. The ECTS uses a thermistor whose resistance changes with temperature.

The electrical resistance of the ECTS decreases as the temperature increases, and vice versa. The reference +5V is supplied to the ECTS via a resistor in the ECM. That is, the resistor in the ECM and the thermistor in the ECTS are connected in series. When the resistance of the thermistor in the ECTS changes with the engine coolant temperature, the output voltage also changes.

During cold engine operation, the ECM increases the fuel injection time and controls the ignition timing based on engine coolant temperature to avoid engine stalling and improve drivability.