GMC Sierra 2005 Owner's Manual page 74

Single Stage vs. Dual Stage Airbags
Depending on the weight of your vehicle you will have
either "Single Stage Airbags" or "Dual Stage Airbags".
Vehicles that have a passenger sensing system
also have dual stage airbags. If the rearview mirror in
your vehicle has a passenger airbag status indicator
printed on it, your vehicle has the passenger sensing
system and therefore, it has dual stage airbags. If
the rearview mirror in your vehicle does not have a
passenger airbag status indicator printed on it, then your
vehicle does not have the passenger sensing system
and it has single stage airbags. See Passenger
Airbag Status Indicator on page 3-35 or Passenger
Sensing System on page 1-74.
1-68
Dual Stage Airbags
If your vehicle has frontal airbags with dual stage
deployment, the amount of restraint will adjust according
to crash severity. Your vehicle is equipped with
electronic frontal sensors which help the sensing system
distinguish between a moderate and a more severe
frontal impact. For moderate frontal impacts, these
airbags inflate at a level less than full deployment. For
more severe frontal impacts, full deployment occurs.
If the front of your vehicle goes straight into a wall
that does not move or deform, the threshold level
for the reduced deployment is about 10 to 16 mph
(16 to 25 km/h), and the threshold level for a full
deployment is about 20 to 25 mph (32 to 40 km/h).
(The threshold level can vary, however, with specific
vehicle design, so that it can be somewhat above
or below this range.)
Vehicle's with dual stage airbags are also equipped
with special sensors which enable the sensing system
to monitor the position of both the driver and passenger
front seats. The seat position sensor provides
information which is used to determine if the airbags
should deploy at a reduced level or at full deployment.