2003 GMC Yukon Owner's Manual - Page 442

Secondary Latch System Your vehicle has an underbody mounted tire hoist assembly equipped with a secondary latch system. It's designed to stop the spare tire from suddenly falling off your vehicle. For the secondary latch to work, the spare must be installed with the valve stem pointing down. See "Storing a Flat or Spare Tire, Jack and Tools" earlier in this section. {CAUTION: Before beginning this procedure read all the instructions. Failure to read and follow the instructions could damage the hoist assembly and you and others could get hurt. Read and follow the instructions listed below. Suburban/Yukon XL F. Retaining Hook A. Bottle Jack G. Retaining Bracket B. Wheel Blocks and Wing Nut C. Wing Nut Holding H. Tool Kit with Jack Tire Blocks Tools and Gloves D. Mounting Bracket E. Removable Tray 5-84