GM Service Manual Online
For 1990-2009 cars only

Your vehicle is equipped with a Retained Accessory Power (RAP) feature which will allow the radio to continue to work up to 10 minutes after the ignition is turned to OFF.

Your radio will work when the ignition key is in ON or ACCESSORY. Once the key is turned from ON to OFF, the radio will continue to work for up to 10 minutes or until any door is opened.