GM Service Manual Online
For 1990-2009 cars only

Your vehicle is equipped with a Retained Accessory Power (RAP) feature which will allow certain features on your vehicle to continue to work up to 20 minutes after the ignition key is turned to OFF.

Your radio will work when the ignition key is in RUN or ACCESSORY. Once the key is turned from RUN to OFF, these features will continue to work for up to 20 minutes or until a door is opened.