2014 LT program car, Pull Me Over Red, 1.4T Auto
XM works fine, just AM/FM is an issue. As for antenna types there seems to be at least two types. I have the larger of the two on my 2014.Yes. Attached is a pic of mine, in case there are other types.
If I understand correctly, this antenna does XM as well as AM and FM. If that's so, then there has to be some sort of low noise amplifier (LNA) in or near the antenna base for the XM. I'm not an RF guy - I can barely spell it - but what I've picked up over the years is that, for satellite radios such as XM, the RF amplifiers need to be right at the antenna. If that's the case here, I'm wondering if your amp is/was bad.
But, without having torn into it, I'm speculating for now. Interestingly, my Haynes has two radio drawings, but neither show an amp on the coax - don't know what to make of that.
As for mine, looking at the antenna, I see a couple spots where moisture could get in there to affect it. But I need to take it apart in hopes of confirming that.