Circuit/System Description
WARNING: This page is about a different car, the 2007 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) provides a low side drive output that controls the trunk relay. The BCM monitors the voltage level on the trunk release relay control circuit to determine when a failure has occurred. The voltage level on this circuit should be high while the trunk relay is not energized, that is; the trunk release feature has not been activated. Voltage will be near 0 volts when the relay is energized. When the BCM receives a trunk release signal from a switch or keyless entry transmitter, it responds by applying ground to the trunk release relay control circuit, which energizes the trunk relay.