Same for me, connecting via a Dension adaptor for a 5 year old Mazda 6.
The audio just comes out of the phone speaker now. Nothing through the car speakers any more.
iOS 6.1 broke something with the audio output. I'm really upset about this.
Anyone got any clues as to what to do?
I tried to downgrade to 6.0.1, but there isn't any way to do that as Apple do not allow it.