Instrument Panel Cluster (IPC) Description and Operation: Voltmeter
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
The IPC displays the system voltage as detected at the ignition 1 input of the IPC. The voltage on the volt gage is also displayed on the DIC. The IPC displays high or low voltage on the DIC when the IPC detects voltage levels out of range.