GM Service Manual Online
For 1990-2009 cars only

This feature turns on the courtesy lamps and the backlighting to the door switches and to the exterior lamp control when a door is opened or if you press the remote keyless entry transmitter unlock button. If activated due to the transmitter, the lighting will remain active for about 40 seconds. Since the entry lighting system uses the light sensor, it must be dark outside in order for the courtesy lamps to turn on. The courtesy lamps turn off approximately 25 seconds after the last door is closed. They will dim to off if the ignition key is turned to RUN, or immediately deactivate if the power locks are activated.