GMC Terrain 2018 Owner's Manual page 103

102 Seats and Restraints
3. Pick up the latch plate, and run
the lap and shoulder portions
of the vehicle's seat belt
through or around the restraint.
The child restraint instructions
will show you how.
Tilt the latch plate to adjust the
belt if needed.
4. Push the latch plate into the
buckle until it clicks.
Position the release button on
the buckle, away from the child
restraint system, so that the
seat belt could be quickly
unbuckled if necessary.
5. Pull the shoulder belt all the
way out of the retractor to set
the lock. When the retractor
lock is set, the belt can be
tightened but not pulled out of
the retractor.