GMC 2003 C4C042 Owner's Manual page 130

Inter Axle Differential Lock Control
-
(If Equipped)
If you're approaching a slippery surface where it looks
like one or even all of the wheels may start to slip, you
can press the bottom of this switch. It locks your rear
differentials so that power is transmitted equally to both
rear axles.
If your vehicle has this
feature, the switch is located
in the center of the
instrument panel.
Let up on the accelerator before you turn on your
-
inter axle differential lock. When you turn on this
control, the diff lock indicator on the center of the
instrument panel will light.
NOTICE:
-
Activating the inter axle differential lock when
the rear wheels are actually spinning freely, as
they might on ice or snow, can cause you to lose
control of the vehicle. It can also damage the
axles. Turn on this control only when the wheels
are not spinning freely.
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