2009 GMC Yukon Owner's Manual - Page 224

Voltmeter Gage When the engine is not running, but the ignition is 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 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 3-64 and Charging System Light on page 3-39 for more information. 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. The gage may also read low during the fuel economy mode, this is normal. Brake System Warning Light With the ignition on, the brake system warning light comes on when the parking brake is set. If the vehicle is driven with the parking brake engaged, a chime sounds when the vehicle speed is greater than 5 mph (8 km/h). The vehicle's hydraulic brake system is divided into two parts. If one part is not working, the other part can still work and stop the vehicle. For good braking, both parts need to be working well. 3-40