GM Service Manual Online
For 1990-2009 cars only

The lamps inside your vehicle will go on when you open any door. These lamps will fade out after about 10 seconds after all of the doors have been closed or when the ignition is turned to ON. These lamps will also go on when you press the trunk release, unlock symbol button or the horn symbol on the keyless entry system transmitter.

The lamps inside your vehicle will stay on for about 10 seconds after your key is removed from the ignition to provide an illuminated exit.