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

PRINCIPLE OF OPERATION, ENGINE COOLANT TEMPERATURE SENSOR





Engine coolant temperature sensor--is located in the intake manifold between the inlet pipes of cylinders 2 and 3 and is in communication with the engine coolant. The sensor is of NTC type.

The control module measures the engine coolant temperature by applying 5 V to the sensor from pin 68 via a built-in 2.74 kohms resistor. The sensor is grounded via pin 67 of the control module.

To ensure accurate temperature measurement, reference ground is supplied to pin 66 of the control module from the sensor ground lead. The voltage across the resistor in the control module is proportional to the engine coolant temperature.

This voltage is used to determine fuel injection duration for pre-injection as well as for cold starting and fuel enrichment during engine warm-up. Engagement of oxygen (Lambda) control and idling speed also depends on engine coolant temperature.

If the sensor is unserviceable or if there is no continuity in the circuit, the control module will use a default temperature of 26°C and the CHECK ENGINE malfunction indicator lamp (MIL) in the main instrument display will light up.

Cars with Electronic Throttle System (ETS)--the engine coolant temperature sensor contains two NTC resistors which are both grounded via the body of the sensor.

One of the NTC resistors is used by the ETS to control idling speed, which is dependent on the engine coolant temperature. The other NTC resistor is used by the Trionic system.

Reference ground from grounding point G7S is connected to pin 66 of the control module. This enables the control module to measure engine coolant temperature with extra precision.