GMC 2007 Yukon XL Owner's Manual page 103

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 passenger's airbag.
CAUTION:
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If the airbag readiness light in the
instrument panel cluster ever comes on
and stays on, it means that something
may be wrong with the airbag system.
If this ever happens, have the vehicle
serviced promptly, because an adult-size
person sitting in the right front
passenger's seat may not have the
protection of the frontal airbag. See
Airbag Readiness Light on page 227 for
more on this, including important safety
information.
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