Just some FYI comments on my base coupe 2011 Bose/OnStar upgrade project using new Pioneer 3300BT head unit. I thought I had a bad HU initially very poor reception, mostly static. Finally figured out it was an antenna problem. I actually first got it working by just leaving the short extension in the radio antenna port and then grabbing that, wham music. I tried various "hidden" antennas, one amplified, one not, very poor results, I don't recommend those. I read many many posts and FAQs on this, none of it worked for me. Maybe something changed in 2011? Maybe some combo of my HU, Bose system, OnStar system? Anyway the 12V+ added to pin B3 actually made static worse, minimal reception, then I tried the 5V+ mod to A4, no help. I tried various combinations of those two mods, no help. In frustration I grabbed an old metal fixed mast Camaro antenna, plugged that in, radio worked fine. So eventually I mounted a 30" fixed length antenna horizontally in the rear of the hatch up against the back plastic/fiberglass below the hatch lock mechanisms, grounded the base of it to a bolt on the hatch lock mount, ran an extension antenna wire up to the radio, plugged that in, fairly good reception.
I have no idea why none of the mods would made my stock antenna function with my Pioneer HU. Anyone know?