2002 GMC Envoy Owner's Manual - Page 147

Charging System Indicator Light The charging system 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. 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. It could indicate that you have problems with a generator drive belt, or another electrical problem. Have it checked right away. Driving while this light is on could drain your battery. 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. Voltmeter Gage When your engine is not running, but the ignition is on (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. Readings between the low and high warning zones indicate the normal operating range. 2-78