2007 GMC Yukon Owner's Manual - Page 231

Voltmeter Gage When your engine is not running, but the ignition is in RUN, this gage shows your battery's state of charge in DC volts. When the engine is running, the gage shows the condition of the charging system. The charging system regulates voltage based on the state of the battery for improved fuel economy and battery life. The gage may transition from a higher to lower or a lower to higher reading, this is normal. Readings between the low and high warning zones indicate the normal operating range. 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 at an idle for an extended period. This condition is normal since the charging system is not able to provide full power at engine idle. As engine speeds are increased, this condition should correct itself as higher engine speeds allow the charging system to create full power. If there is a problem with the battery charging system, this light will come on or the SERVICE BATTERY CHARGING SYSTEM DIC message will display. See DIC Warnings and Messages on page 254 and Charging System Light on page 230 for more information. 231