GMC Sierra Denali 2014 Owner's Manual page 54

3-4 Seats and Restraints
To adjust the power lumbar support:
Press and hold the control
forward to increase or rearward
to decrease upper and lower
lumbar support at the same time.
Press and hold the control up to
increase upper lumbar support
and decrease lower lumbar
support.
Press and hold the control down
to increase lower lumbar support
and decrease upper lumbar
support.
Reclining Seatbacks
To adjust the seatback:
Tilt the top of the control
rearward to recline.
Tilt the top of the control forward
to raise.
Warning
Sitting in a reclined position when
the vehicle is in motion can be
dangerous. Even when buckled
up, the safety belts cannot do
their job.
The shoulder belt will not be
against your body. Instead, it will
be in front of you. In a crash, you
could go into it, receiving neck or
other injuries.
The lap belt could go up over
your abdomen. The belt forces
would be there, not at your pelvic
bones. This could cause serious
internal injuries.
For proper protection when the
vehicle is in motion, have the
seatback upright. Then sit well
back in the seat and wear the
safety belt properly.