Circuit/System Description
WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) monitors the ignition switch. When the key is in the ignition, the ignition switch is closed and the signal circuit is low. When the key is not in the ignition, the ignition switch is open and the signal circuit is high.