GMC 1994 Sonoma Owner's Manual page 143

driver could. With rear-wheel anti-lock: If one of the rear wheels is about
to stop rolling, the computer will work the brakes at the rear wheels. The
computer is programmed to make the most of available tire and road
conditions.
As you brake, your computer keeps receiving updates on wheel speed and
controls braking pressure accordingly.
Remember: Anti-lock doesn't change the time you need to get your foot up
to the brake pedal. If you get too close to the vehicle in front
of
you, you
won't have time to apply your brakes if that vehicle suddenly slows or
stops. Always leave enough room up ahead to stop, even though you have
anti-lock brakes.
To Use Four- Wheel Anti-Lock
Don't pump the brakes. Just hold the brake pedal down and let anti-lock
work for you. You may feel the brakes vibrate, or you may notice some
noise, but this is normal.
To Use Rear-Wheel Anti-Lock
Use rear-wheel anti-lock like regular brakes. You may feel the brakes
vibrate, or you may notice some noise outside your vehicle, but this is
normal. Let anti-lock work for you, but remember: Your front wheels can
still
stop rolling. If that happens, release enough pressure
on
the brakes to
get the wheels rolling again so that you can steer.
With the four-wheel drive option, you won't have rear-wheel anti-lock
braking when you shift into four-wheel drive. But you will have regular
braking. When you shift back into two-wheel drive, you will have
rear-wheel anti-lock again.
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