GMC 2006 Sierra 1500 Pickup Owner's Manual page 319

The lights and chime will come on each time the ignition
is turned on until the problem is repaired. See your dealer
for service.
Let us say the road is wet and you are driving safely.
Suddenly, an animal jumps out in front of you. You
slam on the brakes and continue braking. Here is 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.
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