2008 GMC Sierra 1500 Pickup Owner's Manual - Page 176

Charging System Light This light will come on briefly when you turn on the ignition, but the engine is not running, as a check to show you it is working. Voltmeter Gage When your engine is not running, but the ignition is on, this gage shows the battery's state of charge in DC volts. It should go out once the engine is running. If it stays on, or comes on while you are driving, you may have a problem with the charging system. A charging system Driver Information Center (DIC) message may also appear. See DIC Warnings and Messages on page 3-59 for more information. This light could indicate that you have problems with a generator drive belt, or another electrical problem. Have it checked right away. If you must drive a short distance with the light on, be certain to turn off all your accessories, such as the radio and air conditioner. When the engine is running, the gage shows the condition of the charging system. 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. 3-40