The water temperature sensor is typically located near the cylinder head water outlet. It monitors engine coolant temperature by means of an internally mounted thermistor. The thermistor has a negative temperature coefficient (NTC), so its resistance value decreases as coolant temperature rises. The accompanying resistance graph demonstrates this relationship.
The water temperature sensor is required because fuel vaporization is less efficient when the engine is cold. Internal engine friction is also higher during cold operation, increasing operating load. The THW signal is used by the ECU to determine how much fuel enrichment correction is necessary to provide good cold engine performance. In addition to fuel calculations, the THW signal plays a major role is almost every other function that the ECU serves.
The water temperature sensor has a two terminal electrical connector attached to either end of the thermistor element.
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