2003 GMC Yukon Owner's Manual - Page 291

Remember: Anti-lock does not change the time you need to get your foot up to the brake pedal or always decrease stopping distance. If you get too close to the vehicle in front of you, you will not have time to apply your brakes if that vehicle suddenly slows or stops. Always leave enough room up ahead to stop, even though you have anti-lock brakes. Using Anti-Lock Do not pump the brakes. Just hold the brake pedal down firmly and let anti-lock work for you. You may feel the brakes vibrate, or you may notice some noise, but this is normal. apply and release the brake pedal and it may continue to run even after you have removed your foot from the brake pedal. When the supplemental brake assist system is operating, you may hear a motor running or feel a slight vibration in the steering wheel or brake pedal. This indicates that the supplemental brake assist system is working to supply additional vacuum for your vacuum assist power brakes. This is a normal operation of your brake system and does not require that the brake system be serviced. Each time you start your vehicle and accelerate to 10 mph, the supplemental brake assist system will perform a self-diagnostic check of the system and you may hear or feel the supplemental brake assist motor run briefly. While you are driving your vehicle, the supplemental brake assist system monitors itself to ensure that it is operating properly. If there is a problem with the supplemental brake assist system, the SERVICE BRAKE BOOSTER message will be displayed on the Driver Information Center. See DIC Warnings and Messages on page 3-64. If your supplemental brake assist system runs every time you apply and release the brake pedal or you notice that the brake pedal has suddenly become much harder to push and the vehicle takes longer to stop, you should have your vehicle serviced as soon as possible. Braking in Emergencies With anti-lock, you can steer and brake at the same time. In many emergencies, steering can help you more than even the very best braking. Supplemental Brake Assist System If your vehicle has vacuum assist power brakes, it is also equipped with a supplemental brake assist system that supplies additional vacuum to the vacuum brake booster if engine vacuum is reduced. Under certain conditions, the supplemental brake assist system may run briefly after starting your vehicle or when you 4-9