2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 517

Manual Shift Transfer Case A. Fill Plug B. Drain Plug A. Fill Plug B. Drain Plug Active Transfer Case To get an accurate reading, the vehicle should be on a level surface. If the level is below the bottom of the filler plug hole, located on the transfer case, you will need to add some lubricant. Add enough lubricant to raise the level to the bottom of the filler plug hole. Use care not to overtighten the plug. 6-57