Circuit/System Description
WARNING: This page is about a different car, the 2007 Pontiac G5 Pursuit, 2007 Pontiac G5, and 2007 Chevrolet Cobalt. 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 supply voltage circuit of the RDFG relay. The voltage level should be low while the RDFG relay is de-energized. The voltage will be near system voltage when the BCM energizes the RDFG relay.