GMC 2003 Sierra 1500 Pickup Owner's Manual page 288

If there's a problem with
the anti-lock brake system,
this warning light will
stay on. See Anti-Lock
Brake System Warning
Light
on
page 3-41.
Along with ABS, your vehicle has a Dynamic Rear
Proportioning (DRP) system. If there's a DRP problem,
both the Brake and ABS warning lights will come on
accompanied by a IO-second chime. 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's say the road is wet and 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.
4-7