Instrument Panel Cluster (IPC) Description & Operation: Voltmeter
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 Chevrolet Tahoe, 2002 Chevrolet Suburban, and 2002 Chevrolet Avalanche. 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. When the engine is ON, the Gauge should be between 10 and 16 volts.