On an XM radio if you have signal it will always give you the preview channel and be able to access the radio ID regardless of the subscription status. For good signal you need to be able to look to the south and up at about a 10:00 angle with out obstructions. I do not have the factory XM but did put the SiriusXM Onyx EZ vehicle kit on my RT and it runs through the auxiliary input. The antenna is inside the rear trunk mounted to one of the screws that the back rest has the slot and it works good.
I will guess someone pulled on a wire when installing it and not the plug causing 1 or more wire to not be making a connection. I think I saw a video about this when I was looking to put a XM on my RT.

Good luck.