Why does my BB Classic stop working when it connected via bluetooth to the car?

I am only able to make phone calls when I dial / select contacts through my car's telefone system (VW). Since the system ist quite slow I rather use my BB to navigate through my contacts. Also BB Maps doesn't work when connected via bluetooth. My BB tells me "connection error" but I do have connection because I'm able to make calls (trough the VW tel system). It seems my BB looses stand-alone functionality when connected via bluetooth. Technically it should be possible because my iPhone, which I switched for a BB 1 Week ago, could do it. Can I change that in the settings? Any suggestions? Thx!