My 2005 STS is a non stop mess. Bought 2 1/2 years ago and already 9k in repair bills and another 1400 to go of "known" issues. I got a new Ecm and yes they need flashed to VIN. Glad you figured it out. These cars, while beauties, are a money pit if you don't take care of them. I'd like to throttle the previous owner of my car. And the dealer I bought it from.
I just got mine back from the shop today they put the old ecm back in and changed the crankcase sensor then they found a loose wire going to the fuse box.
Yea I did I took it to a shop and they told me it was the cam sensor. This sensor is located under the air intake manifold. I paid them to do it since I had towed it there and didn’t want to tow it back home.