Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Being a used vehicle (I presume? if not, it's a new vehicle and quite simply, take the problem to the dealership - the AVIC would be part of what they sold you, and it would be their responsibility that it *works* when it's sold to you!...) I would presume, since the AVIC deck is in many ways disabled without any specific disability, you quite simply have a defective Pioneer AVIC deck. It will require repair by Pioneer (or, at the dealership, if the Tahoe is new.)
Or, you could replace it.
If you need any further advice on this matter, let me know, please, and I will advise you further.
If you think the AVIC is not really 'broken', then please tell me the error indications, or error messages, or let me know what it *can* do... what you have described so far is a 'broken' device, but if it still functions or appears to have some rational reason for its lack of functions, I will consider that also - and advise you accordingly - if that's how it is.