GMC Terrain 2018 Owner's Manual page 71

70 Seats and Restraints
The lap-shoulder belt may lock
if you pull the belt across you
very quickly. If this happens, let
the belt go back slightly to
unlock it. Then pull the belt
across you more slowly.
If the shoulder portion of a
passenger belt is pulled out all
the way, the child restraint
locking feature may be
engaged. If this happens, let
the belt go back all the way
and start again.
Engaging the child restraint
locking feature in the front
outboard seating position may
affect the passenger sensing
system. See Passenger
Sensing System 0 80.
If the webbing locks in the latch
plate before it reaches the
buckle, tilt the latch plate flat to
unlock.
3. Push the latch plate into the
buckle until it clicks.
Pull up on the latch plate to
make sure it is secure. If the
belt is not long enough, see
Seat Belt Extender 0 73.
Position the release button on
the buckle so that the seat belt
could be quickly unbuckled if
necessary.
4. To make the lap part tight, pull
up on the shoulder belt.