2007 GMC Acadia Owner's Manual - Page 221

Voltmeter Gage When the engine is not running, but the ignition is turned to ON, this gage shows the battery's state of charge in DC volts. Readings in the low warning zone may occur when a large number of electrical accessories are operating in the vehicle and the engine is left idling for an extended period. If there is a problem with the battery charging system, a SERVICE BATTERY CHARGING SYSTEM message will appear in the Driver Information Center (DIC) and/or the charging system light will come on. See DIC Warnings and Messages on page 244 and Charging System Light on page 220 for more information. However, readings in either warning zone may indicate a possible problem in the electrical system. Have the vehicle serviced as soon as possible. When the engine is running, this gage shows the condition of the charging system. The vehicle's charging system regulates voltage based on the state of charge of the battery. The voltmeter may fluctuate. This is normal. Readings between the low and high warning zones indicate the normal operating range. 221