GMC 2006 Envoy Owner's Manual page 76

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.
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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 3-35 for more on this, including
important safety information.