Body Control Module (BCM)
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Rear Defog Relay: The scan tool displays On or Off. When the BCM energizes the RR DEFOG relay, the scan tool will display On. When the BCM de-energizes the RR DEFOG relay, the scan tool will display Off.