A 5-volt voltage is applied to the Engine Coolant Temperature (ECT) sensor output terminal from the ECM/PCM via the resistor in the ECM/PCM. The ground terminal is grounded with ECM/PCM. The engine coolant temperature sensor is a negative temperature coefficient type of resistor. It has the characteristic that when the engine coolant temperature rises the resistance decreases. The engine coolant temperature sensor output voltage increases when the resistance increases and decreases when the resistance decreases.