My boy has a Yukon denali and he has the same problem. Not sure if the navs are similiar but what I hear is you have to add a switch inline with the park to drive sensor. Once you put the car in drive, hit the switch and the radio will still think your in park. I remember reading this awhile ago but look in the Yukon Denali forum and you should be able to find the post. Sorry guys I'm a BMW m3 man but my roommate has the 03 CTS so I'm looking for him. So I hope this has enlightened everyone to find the post....Thanks....Mike