Overview ENGINE CONTROLS - INPUT SENSORS - Autoshop 101
Overview ENGINE CONTROLS - INPUT SENSORS - Autoshop 101
Overview ENGINE CONTROLS - INPUT SENSORS - Autoshop 101
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Input Sensors Used For Injection<br />
and Spark Corrections<br />
Water Temperature Sensor (THW)<br />
The water temperature sensor is typically<br />
located near the cylinder head water outlet. It<br />
monitors engine coolant temperature by<br />
means of an internally mounted thermistor.<br />
The thermistor has a negative temperature<br />
coefficient (NTC), so its resistance value<br />
decreases as coolant temperature rises.<br />
The accompanying resistance graph<br />
demonstrates this relationship.<br />
<strong>ENGINE</strong> <strong>CONTROLS</strong> - <strong>INPUT</strong> <strong>SENSORS</strong><br />
The water temperature sensor is required<br />
because fuel vaporization is less efficient<br />
when the engine is cold. Internal engine<br />
friction is also higher during cold operation,<br />
increasing operating load. The THW signal is<br />
used by the ECU to determine how much fuel<br />
enrichment correction is necessary to provide<br />
good cold engine performance. In addition to<br />
fuel calculations, the THW signal plays a<br />
major role is almost every other function that<br />
the ECU serves.<br />
Page 16 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
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