Engine - Coolant Temperature Sensor/Switch: Description and Operation

The Water Thermosensor, located in the intake manifold, is a thermistor device whose resistance varies with changes in engine coolant temperature. The ECU sends a reference voltage to the sensor and measures changes in resistance as the engine temperature fluctuates. The ECU utilizes this engine temperature information in its calculations for outputs such as air/fuel ratio control and emission devices.

Sensor temperature/resistance relationship is as follows:

COOLANT TEMP. RESISTANCE (K OHMS)

-20°C (-4°F) 14.5 - 17.8
20°C (68°F) 2.2 - 2.7
40°C (104°F) 1.0 - 1.3
60°C (140°F) 0.50 - 0.65
80°C (176°F) 0.29 - 0.35