GM Service Manual Online
For 1990-2009 cars only

The lamps inside the vehicle come on when any door is opened. These lamps will fade out after about 20 seconds after all of the doors have been closed or when the ignition is turned on. These lamps will also go on when you press the trunk release, unlock symbol button or the horn symbol on the Remote Keyless Entry System (RKE) Transmitter.

The lamps inside the vehicle will stay on for about 20 seconds after the key is removed from the ignition to provide an illuminated exit.