GMC YUKON XL 2003 Manual page 296

If you want to use tire chains, the vehicle needs to be in
2 wheel steer mode.
4: In this mode all four wheels will help steer the
vehicle. If you want to use 4, and your vehicle is not in
this mode, press the button, until the 4 indicator,
located to the right of the 4 Wheel Steer button, comes
on and stays on. If the 4 indicator is flashing you will
have to center the steering wheel by turning it to the left
or right.
Slower Speeds (below 40 m.p.h./ 64 km/h )
At slower speeds the front and rear wheels will turn in
opposite directions. This helps the vehicle make
tighter turns, such as during parking, cornering and
turning into tight spaces.
Higher Speeds (40 m.p.h./64 km/h, and above)
At higher speeds the front and rear wheels will turn in
the same direction. This improves stability of the vehicle
during lane changes and sweeping turns.
.q
(4 Wheel Steer tow mode): When towing a
trailer the 4 wheel steer tow mode provides enhancea
stability allowing the trailer to follow the path of the
tow vehicle more closely, especially during lane
changes.
In this mode the system operates much like the 4 mode,
but
is
enhanced for trailer towing. It is recommended
for all types and weights of trailers.
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