Oil Life Monitor
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 PCM/ECM sends the oil life remaining percentage to the body control module (BCM) via a serial data message. The DIC receives a serial data message from the BCM indicating the remaining oil life. The DIC displays the current percentage of the GM Oil Life System as determined by the PCM/ECM.