This may be long and drawn out, but that's how much I've tried troubleshooting and researching.
I have #1 Key Fob 25843982, which came with the car. Everything worked (inc. tailgate). SInce it was in really bad shape, I purchased an aftermarket key from Amazon which had the same FCC ID thinking it was the same. https://www.amazon.com/gp/product/B07MDM136J/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
Well it seemed all 4 key slots were taken (wierd) so I had to do a full relearn on all Keys to program the Original fob as #1 and the new fob as #2. That's when the isues started... NO TAILGATE CONTROL ON BOTH KEYS! Shouldn't the original key I had still work?
So I got a friend's Tech2 and just reprogrammed the liftgate module firmware to latest (just in case) and started looking at the signals. I also found this information online
Got a call from another shop. They are working on this 2010 CTS Wagon & they were at their wits end. The tailgate works from the liftgate handle & driver door switch, but won't open with the key fob. I love torture, so I agree to look at it, after all how hard can it be? The shop left out the...
In it, the guy mentioned looking at the Keyfob signals received ... well it's just like he states! The remote control module receives “R. Cloure Rel." instead of "R. Closure Start" to start the the Liftgate open/close process!
How the heck??? The original remote WORKED before I reprogrammed it, but now sends a wrong signal??? What gives? Ofcours the replacement key also sends this sedan/coupe style signal as could be expected ... but the #1 oriiginal is hard to believe! Only other thing I can do is to also program the remote control module and BCM to make absolutely sure. Although I think they were already the latest firmware.
I'm stumped, and I don't wanna go buying $150 original Fobs until I atleast get the GM key I have working. Prob why the dealer wants to charge me $300+ and 4-5 hrs time to get a new key cut and prorammed? what do they know/do that I can't duplicate here?
BTW, here's also a website that sells keys supposed to work with the Vagons, but a different GM part number is listed (not ... 25843982/25843983 as I've found for the 2012). But when I look up the listed GM PN's under this key, it says
"Exc.Keyless Entry. Exc.Passive Entry. Remote Engine Start." which makes me doubt it'll work as the original PN I have says "Wagon, with passive entry, with remote start, remote 1. Remote Engine Start. Keyless Ignition".