Instrument Panel Cluster (IPC) Description and Operation: Voltmeter
WARNING: This page is about a different car, the 2003 GMC Safari and 2003 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
The IPC displays the battery voltage as determined by the BCM. The IPC receives a class 2 message from the BCM indicating the battery voltage.