Circuit Description
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) monitors the rear defogger switch input. When the rear defogger is turned on, rear defog switch closed, the BCM grounds the coil side of the rear defog relay. This will energize the relay activating the rear defogger.
The first time in an ignition cycle that the rear defogger is activated, the rear defogger will remain on for 15 minutes, or until the ignition switch is turned OFF. If the rear defogger is activated again during the same ignition cycle, the rear defogger will remain on for 7 1/2 minutes, or until the ignition switch is turned OFF.