2005 GMC Envoy Owner's Manual - Page 173

If, after several seconds, all status indicator lights remain on, or if there are no lights at all, there may be a problem with the lights or the passenger sensing system. See your dealer for service. Charging System 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. {CAUTION: If the off indicator and the airbag readiness light ever come on together, it means that something may be wrong with the airbag system. If this ever happens, have the vehicle serviced promptly, because an adult-size person sitting in the right front passenger seat may not have the protection of the frontal airbag. See Airbag Readiness Light on page 3-35. 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. 3-37