GMC 1994 Yukon Owner's Manual page 166

Anti-Lock Brakes (ABS)
Your vehicle has an advanced electronic braking system that can help you
keep it under control. When you start your vehicle and begin to drive away,
you may hear a momentary motor or clicking noise. This is the ABS system
testing itself.
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. 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 the 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. You can steer around
the obstacle while braking hard.
As you brake, your computer keeps receiving updates on wheel speed and
controls braking pressure accordingly.
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