BTW, the CST-V ECU was in front of the driver side tire. You had to get under the car and open up a little 'box' that housed the ECU. There was a 10mm bolt that kept it closed, but it wasnt a truly 'sealed' box, so all sorts of road debris and salt got in there. Once the bolt was removed you just slid the ECU out and detached the 2 harnesses that were there (red and blue).
I havent found the ECU on the STS-V yet, Ill look it up on the GM-SI to see how they recommend removing it.
STS-V ECM is located underneath the air cleaner housing but don't access it from above. Do it from below, it is a lot easier.
CTS-V is in a similar location, also accessed from underneath.
If the dealer reprograms the ECM whatever "tune" you have in it will be erased.
There is no indicator to us that it has been reflashed with a tune, if you want to keep it make sure your dealer knows not to reprogram it without your foreknowledge.
Take the stuff off from underneath the car, I am not sure taking the wheelhouse trim out will get you there.
I have one here in the shop, I'll look later and tell you if any of my advice needs to be "modified"
Ah yes, from underneath the car. Well, at least I now know how to remove the air filter assembly
Well, I fought my way into the ecm. You can get to it from above if you take the air cleaner out and you'll find it hiding beneath the horns. One nut removes the horn bracket and you're there. I'm sure it is easier to get to it from below but I already had the filter assembly out ...