Circuit Operation

5 volts are applied to the engine coolant temperature sensor output terminal (terminal No. 1) from the ECM (terminal No. 83 - M/T) or PCM (terminal No. 44 - A/T) via the resistor in the ECM (M/T) or PCM (A/T). The ground terminal (terminal No. 2) is grounded with ECM (terminal No. 92 - M/T) or (terminal No. 57 - A/T).
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 resistor increases and decreases when the resistance decreases.