Two people in the past month or so have asked, so let me post the full rundown here:
My Equipment:
2012 Limited Edition with JBL sound. No customization done to audio system
Isolating the issue:
As I mentioned before, I had been in and out of the dealership trying to figure out the issue. I was getting a "No Signal" error on the radio.
At my latest dealership service appointment, they told me they think the XM control unit is faulty and I need a new one. Not wanting to drop $2k on the issue I dug in myself and noticed that when I unplugged the antenna from the control unit, my error switched from "No Signal" to "Check Antenna". I ordered a replacement (refurbed) control unit and was getting the same errors. Ordered replacement antenna and problem solved
Parts:
Details:
For me, that control unit sits under the front passenger seat.
All the connections are facing forward, so you can carefully peel back the carpet (with the seat moved all the way back) and expose them. The antenna dongle is the gray one (smallest). I swapped the shark fin for the new one and ran the cable under the carpet, up the a-frame pillar and behind the dash. My new antenna sits next to the front passenger speaker and is held there with a little double sided tape. Yes, I could have put the antenna on the exterior, but I didn't want to make any holes or deal with waterproofing, and the new setup is strong enough that the windshield doesn't cause any signal loss.
I also didnt replace the shark fin, because: fool me once, shame on you; fool me twice... OEM fin replacement is ~$250+ for a part we know will deteriorate again. No thanks...