GMC 2010 Sierra Denali Owner's Manual page 81

Some child restraints that have a top tether are
designed for use with or without the top tether
being attached. Others require the top tether always
to be attached. In Canada, the law requires that
forward-facing child restraints have a top tether, and
that the tether be attached. Be sure to read and follow
the instructions for your child restraint.
If the child restraint does not have a top tether, one can
be obtained, in kit form, for many child restraints. Ask
the child restraint manufacturer whether or not a kit is
available.
Lower Anchor and Top Tether Anchor
Locations
Rear Seat
(Top Tether Anchor): Seating positions with top
tether anchors.
(Lower Anchor): Seating positions with two lower
anchors.
The rear outboard seating positions have exposed
metal lower anchors located in the crease between the
seatback and the seat cushion.
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