GMC Denali 2004 Owner's Manual page 82

For some children who have outgrown child restraints
and for very small adults, the passenger sensing system
may or may not turn off the right front passenger's
frontal air bag, depending upon the person's seating
posture and body build. Everyone in your vehicle
who has outgrown child restraints should wear a safety
belt properly — whether or not there is an air bag
for that person.
If a person of adult-size is sitting in the right front
passenger's seat, but the off indicator is lit, it could be
because that person is not sitting properly in the seat or
the air bag off switch is in the off position. If this
happens and the switch is in the proper position, turn
the vehicle off and ask the person to place the seatback
in the fully upright position, then sit upright in the
seat, centered on the seat cushion, with the person's
legs comfortably extended. Restart the vehicle and have
the person remain in this position for about two minutes.
This will allow the system to detect that person and
then enable the passenger's air bag.
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