2009 GMC Envoy Owner's Manual - Page 177

The service four-wheel drive light comes on to indicate that there may be a problem with the drive system and service is required. Malfunctions can be indicated by the system before any problem is apparent, which may prevent serious damage to the vehicle. This system is also designed to assist your dealer in correctly diagnosing a malfunction. Gate Ajar Light If this light comes on, the liftgate or liftglass is not completely shut. Check Gages Warning Light The check gages light will come on briefly when you are starting the engine. Close the liftgate or liftglass. Never drive with the liftgate or liftglass even partially open. If the light comes on and stays on while you are driving, check your coolant temperature and engine oil pressure gages to see if they are in the warning zones. 3-45