GMC Sierra Denali Classic 2007 Owner's Manual page 76

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 airbag, 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 airbag 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. If this happens, 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 right
front passenger's airbag.
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