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Cabin temperature sensor

Cabin temperature sensor





The cabin temperature sensor is located in the roof panel by the rear-view mirror and is of the NTC type. It is supplied with 5 V from pin 20 via a 10 kOhm resistor integrated in the ACC unit and is grounded from pin 39. The voltage over the sensor is therefore inversely proportional to the temperature (the voltage decreases when the temperature increases). The value is used to calculate the current temperature at head height for the front seat passenger and driver. The following default values are also used:


• outside temperature

• time since engine last ran

• time since start

• mixed-air temperatures

• fan speed

• solar irradiance


The cabin temperature sensor value is only a small part of the calculation, at the most 30% at a temperature below 23°C and at least 0 % at a temperature above 25°C. The calculated temperatures are then compared with those that the driver and the passenger set on the ACC unit display. The set temperatures are slightly corrected with regards to outside temperature so that the experienced temperature will match the set temperature.

As soon as a difference occurs, the mixed-air temperature must be increased or decreased. The control module turns the air-mixing flap in question until the required mixed-air temperature is achieved.

Diagnostics

In the event of an open circuit or short circuit, diagnostic trouble code B1350 is set and 02 is displayed instead of right-hand temperature when calibrating.

The outside temperature is used as a default value when the ignition is turned on and then the mean value of the calculated temperatures at head height for the front seat passenger and driver.