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

Coolant Temperature Sensor

The temperature sensor is placed in the left end of the cylinder head and is in contact with the engine coolant. The sensor is of NTC type.

The control module measures the coolant temperature by supplying the sensor with 5 V from pin 39 via an integral 1.0 kohm resistor. The sensor is grounded via control module pin 22. The voltage across the resistor in the control module is proportional to the temperature of the coolant.

The coolant temperature is used to:
- calculate the injection time for pre-injection
- calculate the injection time during starter motor cranking
- calculate after-starting enrichment
- determine when the closed loop control system should be engaged
- correct the idling speed.

Diagnostics
- If the sensor voltage is too low, diagnostic trouble code P0117 will be generated.
- If the sensor voltage is too high, trouble code P0118 will be generated.

System reaction to a fault
- A substitute temperature is selected which is equal to the intake air temperature on starting and is then increased by 1.0°C (1.8°F) every 150 engine revolutions.
- Purging is blocked.