GMC 2010 Yukon/Yukon XL Owner's Manual page 227

If the turn signal is left on for more than 3/4 of a mile
(1.2 km), a chime will sound at each flash of the turn
signal and the message TURN SIGNAL ON will also
appear in the Driver Information Control (DIC). To turn
the chime and message off, move the turn signal lever
to the off position.
change the headlamps from low to high beam, push
the lever toward the instrument panel. To return to
low-beam headlamps, pull the multifunction lever toward
you. Then release it.
To
When the high beams are
on, this indicator light on
the instrument panel
cluster will also be on.
This feature lets you use the high-beam headlamps to
signal a driver in front of you that you want to pass.
It works even if the headlamps are in the automatic
position.
To use it, pull the turn signal lever toward you, then
release it.
If the headlamps are in the automatic position or on
low beam, the high-beam headlamps will turn on. They
will stay on as long as you hold the lever toward you.
The high-beam indicator on the instrument panel cluster
will come on. Release the lever to return to normal
operation.
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