2003 GMC 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