GM Service Manual Online
For 1990-2009 cars only

Your vehicle has a Retained Accessory Power (RAP) feature which will allow the radio, wipers, power windows, sunroof and the rear power outlet to work after the ignition is turned off.

Your radio will work when the ignition key is in RUN or ACC (Accessory). Once the key is turned from RUN to LOCK, the radio will continue to work for up to 10 minutes or until any door is opened.