I think I found your problem, your deck is probably "part pontiac vide radio"
A search of that part number 12207139 shows me everything pointing to a pontiac vide radio, if you notice in the following auction the band button does not show "band" but shows "amfm" this would mean it's not xm capable.
PONTIAC VIBE RADIO 2003 2004 AM FM SIX CD 12207139 | eBay
Basically what I think happened is Explicit_Spade bought it without knowing it was rebuilt.
Basically 6 disc changers in grand prix are rarer. so as mentioned earlier i suspect the original seller had a defective gp6 disc and either used the backend parts from the vibe radio to rebuild the gp one or simply put the GP 6disc face on the vibe one.
The rebuilder would have never realized this issue just from testing it on the bench alone.
Before we confirm this is really the case do the connector and battery thing ,if this dont work try your single disc. If the xm come back with the single disc you will have to get another 6 disc from a true GP.
If you get another 6 disc from say ebay I would install it again, and go to the dealer with it locked and try to get them to unlock it complimentary for you.
I know it's frustrating to get one of these decks, but you can trust that if you had a true gp deck everything would have worked![]()