Factory TNR-no volume
 

I bought a factory GM TNR nav radio on ebay. Part number: 15230099 which I believe is the second revision TNR. Went to the dealership today to have the passlock programmed to my VIN. Everything went fine but there is no volume. When the volume dial is turned or the volume button on the steering wheel is used they do nothing. Doesn't even show a volume bar or anything like that. I have no sound what so ever.

Any ideas? The service guy said to check the connections at the back of the radio but given how hard those things click in I would be really surprised if that was the problem.

I do have the Y91 RPO code which the service guy said if the radio wasn't compatible they wouldn't have been able to program it so that should be able to be ruled out.

Thanks in advance!