GMC Envoy Owner's Manual page 61

Your vehicle may or may not have a roof-mounted
airbag and rollover sensor. See Airbag System
on page 1-48. These "rollover capable" airbags are
designed to inflate in moderate to severe side crashes
or during a rollover. A side impact airbag will inflate
if the crash severity is above the system's designed
"threshold level." The threshold level can vary with
specific vehicle design. Side impact airbags are not
designed to inflate in frontal or near-frontal impacts, or
rear impacts, because inflation would not likely help
the occupant.
Your vehicle has seat position sensors which enable the
sensing system to monitor the position of the driver's
seat and the right front passenger's seat. Seat position
sensors provide information that is used to determine
if the airbags should deploy at a reduced level or at full
deployment.
1-54
In any particular crash, no one can say whether an
airbag should have inflated simply because of the
damage to a vehicle or because of what the repair costs
were. For frontal airbags, inflation is determined by
the angle of the impact and how quickly the vehicle
slows down in frontal and near-frontal impacts. For side
impact airbags, inflation is determined by the location
and severity of the impact.
The airbag system is designed to work properly under a
wide range of conditions, including off-road usage.
Observe safe driving speeds, especially on rough
terrain. As always, wear your safety belt. See Off-Road
Driving with Your Four-Wheel-Drive Vehicle on
page 4-16 for tips on off-road driving.