Chevrolet Silverado Classic 2007 Owner's Manual page 100

The passenger sensing system is designed to
enable (may inflate) the right front passenger's
frontal airbag anytime the system senses
that a person of adult size is sitting properly in the
right front passenger's seat. When the passenger
sensing system has allowed the airbag to be
enabled, the on indicator will light and stay lit to
remind you that the airbag is active.
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.
100
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.