GMC Chevrolet Tahoe 2003 Manual page 303

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.
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 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.
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