Circuit Description
WARNING: This page is about a different car, the 2004 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
The Body Control Module (BCM) monitors the voltage level on the control circuit of the RR DEFOG relay. The voltage level should be near system voltage while the RR DEFOG relay is de-energized. The voltage will be pulled low when the BCM energizes the RR DEFOG relay. The BCM test the control circuit of the RR DEFOG relay while the relay is de-energized.