Pontiac 2003 Montana Owner's Manual page 92

An unfastened shoulder harness clip won't
help keep the harness in place on the child's
shoulders. If the harness isn't on the child's
shoulders, it won't be able to restrain the
child's upper body in a sudden stop or crash.
The child could be seriously injured. Make
sure the harness clip is properly fastened.
12. Pull the shoulder harness adjustment strap (C)
firmly until the harness is snugly adjusted around
the child. You should not be able to put more than
two fingers between the harness and the child's
chest. Make sure the harness and buckle strap are
not twisted.
1-85