Engine - Coolant Temperature Sensor/Switch: Description and Operation

Water Thermosensor:

PURPOSE
Signal ECU of changes in engine (coolant) temperature. The ECU uses engine temperature information in its calculations for outputs such as air/fuel ratio control, ignition timing, turbo control, and emission devices.

LOCATION
On top of engine near thermostat housing.

OPERATION
Sensor is a thermistor device whose resistance varies with changes in engine coolant temperature. The ECU sends sensor a reference voltage and measures changes in resistance as engine temperature fluctuates.

Sensor temperature/resistance relationship:

COOLANT TEMP. RESISTANCE (K OHMS)

-20°C (-4°F) 14.6 - 17.1
20°C (68°F) 2.2 - 2.7
80°C (176°F) 0.30 - 0.35