I have a 2012 base. Do I need the separate XM antennae or does it work through the On Star? Thanx

 

XM has it's own antenna.

 

Yep. but if the car did not come with XM, then will not have the XM antenna in the side mirror.

So if your adding XM to a stock radio, then SIR-gm1 kit will come with an anttena as well (if you can find a new one).

Short version, pull the carpet back from above the drivers rear wheel well in the car, and your going to find the factory location for the module.
http://www.kawal.net/PAL%20rev2%20install.htm

The kit will come with a connector that connects to the module and then to factory connector. Also, the kit will come with the antenna, so you pull one of the rear tail lights, mount the antenna in the rear fender void area, then fish the cable end back up to the module so you can plug it in to the module as well. Once you have the two connected, then bolt the module into the factory location.

The next one gets a little trickier, but will need a tech II to active the XM button on the radio itself.

From here, just need to use the button to switch over to XM, pull the serial number off the radio (will be on the module as well) and use that serial number when you are activating XM with Sirus.

As for buying either a used OEM XM module, or used SIR-1, add about $40 to the cost, since you will need to send the module in to be cleared first, so it can marry to your car when you turn it on in your car the first time. Also just a heads up, but the 05 to about 07 factory XM modules may be a hit or miss (will be a dead give away on the price, since they will be selling for around $40. Hence sirus bought out XM in that time frame, and on the older modules, they have to be reprogramed by Sirus to work with their signal. The rub, unless you get a dealer to send the module in to sirus, Sirus will not program it for you directly instead.

 

I finally got it working. The car wasn't the problem, trying to get someone at Sirius to listen, was. About the car, if you have RPO #U2K the antennae is in place and I didn't need any other equipment.