Inter-Axle Differential Lock Control; Traction Control System (Tcs) - GMC 2003 GMT560 T-Series Owner's Manual

Inter-Axle Differential Lock Control

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.
4-10
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 snow or ice, 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.

Traction Control System (TCS)

Your vehicle may have a traction control system that
limits wheel spin. This is especially useful in slippery
road conditions. The system operates only if it senses
that one or both of the rear wheels are spinning or
beginning to lose traction. When this happens,
the system applies the brake(s) at the affected wheel(s).
The bottom light on the TCS on/off button will come
on when the TCS is limiting wheel spin. You may feel or
hear the system working, but this is normal. The TCS
will function at speeds up to about 25 mph (42 km/h).