2004 GMC Envoy Owner's Manual - Page 159

Charging System Light {CAUTION: If the air bag readiness light stays on after you start your vehicle, it means the air bag system may not be working properly. The air bags in your vehicle may not inflate in a crash, or they could even inflate without a crash. To help avoid injury to yourself or others, have your vehicle serviced right away if the air bag readiness light stays on after you start your vehicle. The air bag readiness light should flash for a few seconds when you turn the ignition key to RUN. If the light doesn't come on then, have it fixed so it will be ready to warn you if there is a problem. 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. 3-39