Chevrolet 2004 Tahoe Owner's Manual page 314

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.
4-18
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.