GMC Sierra 2018 Owner's Manual page 121

120 Seats and Restraints
7. If your child restraint has a top
tether, follow the child restraint
manufacturer's instructions
regarding the use of the top
tether. See Lower Anchors and
Tethers for Children (LATCH
System) 0 96 for more
information on using the top
tether anchors.
8. Before placing a child in the
child restraint, make sure it is
securely held in place. To
check, grasp the child restraint
at the seat belt path and
attempt to move it side to side
and back and forth. When the
child restraint is properly
installed, there should be no
more than 2.5 cm (1 in) of
movement.
To remove the child restraint,
unbuckle the vehicle seat belt and
let it return to the stowed position.
If the top tether is attached to a top
tether anchor, disconnect it.