[Lampoon]

Do you have a stock XM antenna on your roof?
See XM when you toggle through your source button?

There is an external (to the radio) XM module you would need.
Also the wiring, and antenna. Then you would need it to be programmed.

I havent done it....as I ordered my car with it but it can be done.

Module

Antenna

As for the wiring to the module/antenna you could ask the people who are selling the module as they removed it from the car. Or you could hit a junkyard....

Dealership to program head unit.

 

[Lampoon]

what year is your G6?

 

[Lampoon]

they hadnt merged the antennas yet by 05.
The XM was in back on top and the onstar was up front on top.

half way through 06 they merged them into one "shark fin" located up front on top.

Soooooo if your roof has no antenna on its back side = no XM.