2003 GMC Envoy Owner's Manual - Page 370

Getting undera vehicle when it is jacked up is dangerous. If the vehicle slips the jack you off could be badly injured or killed. Never get under a vehicle when is supported only by a jack. it I L Rear A. B. C. D. E. Frame Jack Handle Extension(s) WheelWrench 4. Place the jack in the appropriate position nearest the flat tire. Raising your vehicle with the jack improperly positioned can damage the vehicle and even make the vehicle fall. To help avoid personal injury and vehicle damage, be sure to fit the jack lift head into the proper location before raising the vehicle. 5-75