I'm asking this on behalf of a friend who owns a 2004 Silverado. My 99 'Burb doesn't have this feature. The newer models, when you turn the key off the radio still plays and all of that until you open the door. In my friend's truck, when you open the door nothing turns off, so it just keeps running and eventually drains the battery. I assume this is a relay or something, but I don't have a manual for his truck, and I knew someone on here would probably know. I appreciate the help.