Buick Enclave 2008 Owner's Manual page 77

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 and seat-mounted side impact 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, remove any
additional material from the seat cushion, 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 two to three minutes. This will allow
the system to detect that person and then enable
the right front passenger's frontal airbag and
seat-mounted side impact airbag.
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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.