Global Machinery Company Sierra 1999 - Manual (Page 198)

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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. 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.
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.