GMC Yukon Owner's Manual page 136

If this happens, use the following steps to allow the
system to detect that person and enable the right front
passenger frontal airbag:
1. Turn the vehicle off.
2. Remove any additional material from the seat,
such as blankets, cushions, seat covers, seat
heaters, or seat massagers.
3. Place the seatback in the fully upright position.
4. Have the person sit upright in the seat, centered
on the seat cushion, with legs comfortably
extended.
5. Restart the vehicle and have the person remain in
this position for two to three minutes after the on
indicator is lit.
2-98
Additional Factors Affecting System
Operation
Safety belts help keep the passenger in position on the
seat during vehicle maneuvers and braking, which helps
the passenger sensing system maintain the passenger
airbag status. See Safety Belts and Child Restraints
in the Index for additional information about the
importance of proper restraint use.
If the shoulder portion of the belt is pulled out all the
way, the child restraint locking feature will be engaged.
This may unintentionally cause the passenger sensing
system to turn the airbag off for some adult size
occupants. If this happens, let the belt go back all
the way and start again.