Cabin Temperature Sensor / Switch: Description and Operation

Temperature Sensor, Cabin Air (218)

Location
Temperature sensor, cabin air (218).

Main task
The sensor provides information regarding the current cabin air temperature.







Type
The cabin temperature sensor is an NTC sensor encased in glass.







Connect
Sensor pin 3 has an internal ACC unit ground connection via pin 12 (K18) and sensor pin 2 receives a 5 V feed from pin 5 (K18) via an integrated 19.6 kOhm resistor in the ACC unit.











NTC resistor characteristics allow the resistance to decrease as the temperature rises. This means that the voltage fed over the resistor also decreases as the temperature rises.

The voltage level from the A/D sensor is converted and is then available in digital form. The digital voltage level is then converted to a temperature value which is stored in the ACC unit operating memory. Voltage levels near 0 V or 5 V are determined as circuit faults.