[Bargeld]

So was the head unit replaced? If so, take it back to the shop that did it and have them fix it.

It sounds like a harness or plug behind the dash wasn't reconnected when it everything was reassembled. Best bet is to remove the head unit and see if anything is flopping around, disconnected back there... Assuming that I understood the situation correctly.

 

[Bargeld]

If nothing was broken before they did work to it, then they should be responsible for any damages. Tell them to order the parts they need to fix it, and then fix it themselves.

But it is probably not a broken part that needs replacement. It is a common occurrence that the airbag wiring gets unplugged and then the car is powered on, which throws a code in the body control management system (i believe). It is typically necessary to have a dealer clear that code, but it does not require any parts to fix.

I would definitely lean on the shop to take responsibility here. Standard procedure for almost all electrical work (and a lot of mechanical work) is step 1: disconnect battery. They either skipped that step or they missed a harness or plug and they turned the vehicle on while the airbag was unplugged. Either way, it is 100% their fault, as long as it wasn't a pre-existing condition before head unit install. Get them to admit that. Then get them to admit they can't fix it themselves. Then get them to agree to cover the cost of the dealer repairing it for them. A good business will have an insurance policy that will cover this for them if the cost is excessive.