GMC 2007 Yukon XL Owner's Manual page 322

Parental Control
The Rear Seat Entertainment System may have a
Parental Control feature, depending on which
radio you have. The Parental Control feature will
turn off the video screen and Rear Seat Audio
(RSA). This feature also disables all button
operations from the remote control and all audio
button operations from the RSA. This feature
can be used to gain the attention of the rear
passengers that are using headphones.
To enable Parental Control press and hold the radio
power button for more than 2 seconds. If on, the
radio, video screen, and RSA will turn off. If a DVD
and/or CD is playing, it will be stopped. A "padlock"
icon or a text message may be displayed on the
radio display depending on which radio you have,
while Parental Control is on. The radio can be
turned back on with a single press of the power
button and used normally, but the RSE system will
remain in Parental Control.
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To turn off Parental Control, press and
hold the radio power button for more than
2 seconds. The video screen and RSA will return
to the state they were in before Parental Control
was turned on. The "padlock" icon will disappear
from the radio display.
Parental Control can also be turned off by inserting
or ejecting any disc, an ignition cycle, or pressing
the "play" icon on the radio DVD display menu.