GMC 2001 C3 Owner's Manual page 193

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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.
4-8
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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.