Check the relay schematic?

 

I had the same issue a couple of years back. Volvo told me I needed a new head unit, at $1100.00.Too costly in my book. I found an old school car audio store, who said they could repair it for $300. They repaired the issue in my head unit, but it still didn't work. As it turns out, our cars have Fiber Optic loops run in them. If one piece of equipment fails, all in that loop fail as well. So in the front you have the head unit, GPS, Bluetooth, Amp, GPS Screen, and misc electrical items. ie: power outlets. We replaced each item in the loop, then returned the ones we didn't need, until we found the bad piece. As it turned out, it was the Blue Tooth unit that was bad. Hopefully you have already resolved your issue, but if not, at least you now have a direction to look at.