Coolant temperature sensor: Notes

Fig 1: Identifying Coolant Temperature Sensor - Control Module Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Identifying Coolant Temperature Sensor - Control Module Communication Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The temperature sensor is located on the left-hand end of the cylinder head and is in contact with the engine coolant. The sensor is NTC type.

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

Engine coolant temperature is used to:

• calculate the injection duration for pre-injection.
• calculate the injection duration while the starter motor is cranking.
• calculate after-start enrichment.
• determine when closed loop should be engaged.
• correct idling speed.
• blocking certain diagnoses:
  • blocking certain diagnoses when engine coolant temperature is below -7°C.
  • reactivate certain diagnoses when engine coolant temperature has exceeded 60 °C.