Circuit/System Description
WARNING: This page is about a different car, the 2017 Chevrolet Spark. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) monitors the voltage level of the key switch lock and unlock signal circuits. When the key is inserted into the driver door key cylinder and turned to the Lock or Unlock position, a switch within the key cylinder closes causing the voltage to drop within the key switch unlock signal circuit. The BCM will detect the drop in voltage will command the driver door to unlock or for all doors to lock.