Coolant Temperature Sensor/Switch (For Computer): Description and Operation

The coolant temperature sensor, located on the thermostat housing, is a negative temperature coefficient (NTC) thermistor. NTC means that the resistance of the thermistor decreases as the sensed temperature increases. Pin 1 of the sensor is connected to ground through the ECM. The ECM applies 5 volts to pin 2 of the sensor and monitors the voltage across the sensor pins. The theoretical full voltage range is from 5 to 0 volts representing maximum cold to maximum hot.

The ECM converts the monitored voltage into a digital number that relates to an engine coolant temperature. The temperature signal is then used for a number of functions:
- Cranking enrichment.
- Warm-up enrichment.
- Acceleration enrichment.
- Air injection.
- Idle speed control.
- Enable EGR.
- Evaporative canister purge.

NOTE: Other sensor inputs are required for the initiation of most of the above listed ECM functions.

Temperature Versus Resistance And Voltage: