GMC Express 2011 Owner's Manual page 68

3-20 Seats and Restraints
To move it down, pull on the center
adjuster control labeled PULL.
You can move the height adjuster
up just by pushing up on the
shoulder belt guide.
After the adjuster is set to the
desired position, try to move it down
without pushing in to make sure it
has locked into position.
Safety Belt Pretensioners
If the GVWR (Gross Vehicle Weight
Rating) of the vehicle is below
3 855 kg (8,500 lb) then the vehicle
has safety belt pretensioners for the
front outboard occupants. See
Vehicle Load Limits on page 9 12 to
locate the certification label which
contains the GVWR.
Although the safety belt
pretensioners cannot be seen, they
are part of the safety belt assembly.
They can help tighten the safety
belts during the early stages of a
moderate to severe frontal, near
frontal, or rear crash if the threshold
conditions for pretensioner
activation are met. And, if the
vehicle has side impact airbags,
safety belt pretensioners can help
tighten the safety belts in a side
crash or a rollover event.
Pretensioners work only once.
If the pretensioners are activated in
a crash, the pretensioners and
possibly other parts of the safety
belt system will need to be replaced.
See Replacing Safety Belt System
Parts after a Crash on page 3 24.