iphone 5 bluetooth car connection

Hi

Since I upgraded to the iOS 6.1.3 I am still able to make calls in the car via bluetooth, however I am no longer able to listen to music.

Bluetooth is obviously working but the music is no longer being streamed or even detected by the car.

It used to work fine before I upgraded.

Is there a way to downgrade?

or solutions?

Any help welcome.

Thanks