Bluetooth connection of Sony Z3+ and my car disconnects when phone display dims

A

AC Question

Sony Xperia Z3+
Marshmellow 6.0.1

The phone does not automatically connect to the car audio system with 6.0.1 any more. Previously this worked like a charm. Now i need to unlock the display. Only then the connection happens automatically.

Furthermore, the BT connection always breaks when the phone display dims (timeout or me locking the phone up).

Please note that this issue is about traffic safety. Using a phone without the handsfree equipment is not allowed.

I have paired my phone with the car system again but it doesn't change anything - the problem remains. I have not made any changes on the car side (other than paired again).

Any advice?