GMC 2010 Yukon/Yukon XL Owner's Manual page 237

The vehicle has an illuminated entry feature.
When the doors are opened, the dome lamps will
come on if the dome override button is in the extended
position. If the dome override button is pressed in, the
lamps will not come on.
The interior lamps come on when the key is removed
from the ignition. They turn off automatically in
20 seconds. The lights do not come on if the dome
override button is pressed in.
For vehicles with reading lamps they are located on the
overhead console.
To turn on the reading lamps, press the button located
next to each lamp. To turn them off, press the button
again.
The vehicle may also have reading lamps in other
locations. To turn the lamps on or off, press the button
located next to the lamp.
The lamps are fixed and cannot be adjusted.
The vehicle has Electric Power Management (EPM) that
estimates the battery's temperature and state of charge.
It then adjusts the voltage for best performance and
extended life of the battery.
When the battery's state of charge is low, the voltage
is raised slightly to quickly bring the charge back up.
When the state of charge is high, the voltage is lowered
slightly to prevent overcharging. If the vehicle has a
voltmeter gauge or a voltage display on the Driver
Information Center (DIC), you may see the voltage
move up or down. This is normal. If there is a problem,
an alert will be displayed.
The battery can be discharged at idle if the electrical
loads are very high. This is true for all vehicles. This is
because the generator (alternator) may not be spinning
fast enough at idle to produce all the power that is
needed for very high electrical loads.
A high electrical load occurs when several of the
following are on, such as: headlamps, high beams, fog
lamps, rear window defogger, climate control fan at high
speed, heated seats, engine cooling fans, trailer loads,
and loads plugged into accessory power outlets.
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