What kind of sound system do you have?
If its L7 the amp is connected to the most bus .
Anything bad on the most bus breaks the Most Bus Loop.
And that makes all the devices on the Most Bus look bad.
Depending on the year of your car an options there
could be several devices in the loop. TCU , sdars , bmw assist are some of the common ones.
The TCU is the telephone control unit.
The thing that most commonly fails is the L7 amp.
There are some places to get the amp repaired.