GMC 2001 Sierra - Manual (Page 230)

4-8
Here’s how anti - lock works. Let’s say the road is wet.
You’re driving safely. Suddenly an animal jumps out in
front of you.
You slam on the brakes and continue braking.
Here’s what happens with ABS.
A computer senses that wheels are slowing down. If one
of the wheels is about to stop rolling, the computer will
separately work the brakes at each front wheel and at
both rear wheels.
The anti - lock system can change the brake pressure
faster than any driver could. The computer is
programmed to make the most of available tire and
road conditions. This can help you steer around the
obstacle while braking hard.
As you brake, your computer keeps receiving updates on
wheel speed and controls braking pressure accordingly.