GMC 1999 Jimmy Owner's Manual page 16

To return the head restraints to the upright position,
reach behind the seats and pull the head restraint up until
it locks into position.
1-10
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On two door models with an inside mounted spare tire,
the driver's side rear seat head restraint must be lifted
and held upright as the seatback is raised. Otherwise, the
head restraint will hit the spare tire and prevent the
seatback from properly latching.
Push and pull on the head restraints to check that they
have locked in the upright position. If they haven't, have
them fixed immediately.
The rear seat head restraints are adjustable. Push the
button located under the head restraint to raise or lower
it. Slide the head restraint up or down so that the top of
the head restraint in closest to your ears. After releasing
the button, push and pull on the head restraint to make
sure it's locked in place.
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