I know enough to be dangerous on Passkey 2 but not 3 so the only suggestion I have is to browse/join a forum for an 07 era GM make/model with lots of users (Camaro maybe?) and try to find threads where they really got into the details about trying to make the same error message go away. Maybe that will give you the insight you need. I agree with what you stated about the online schematics and info about factory theft protection can conflict or be misleading. But eventually you can filter out the noise and false info to find most of the clues you need. Good luck!
