@Henn28: Yes, it throws a code.

@AndrewWynn: So if the sensor is broken, then the flap should be permanently closed or open when in "auto" mode. Hopefully it's designed to signal "close" when it fails! :-)

Do you know where the flap is located? Can we actually get a look at it without taking stuff apart or even hear it close/open? I am thinking of running a test by sending various voltages manually and see if it activates the mechanism.

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2001 BMW X5 3.0i, Automatic, Gasoline