GM Service Manual Online
For 1990-2009 cars only

If the dome lamp is in the AUTO position, the lamps inside your vehicle will come on when any door is opened. In addition, the lights will come on when the remote keyless entry unlock button is pressed. It will stay on for 20 seconds or until a door is opened. After the door is opened the lights will remain on and stay on for 20 seconds after the doors are closed, or until you put the key in the ignition and turn the key to RUN. The lights will then gradually dim until it is no longer lit.