GMC 2009 Yukon XL Owner's Manual page 491

CAUTION:
{
Getting under a vehicle when it is jacked up is
dangerous. If the vehicle slips off the jack, you
could be badly injured or killed. Never get under a
vehicle when it is supported only by a jack.
CAUTION:
{
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.
6. Take off the flat tire.
5. Remove all of the
wheel nuts.
5-95