GMC T-Series 2007 Owner's Manual page 125

The brake system warning light may come on,
and the warning tone may sound, when you
are turning and braking at the same time. This is
normal. See "Hydraulic Brake Systems" under
Braking on page 152.
When this light comes on, you will also hear
a warning tone. Have the system repaired
immediately.
If this light comes on,
it means there may be
a problem with the
brake system.
Both of these lights should come on briefly every
time you start your engine. If they do not come
on then, have them fixed so they will be ready to
warn you if there is a problem. If one or both
of these warning lights stay on after you start the
engine, there could be a brake problem. Have
your brake system inspected right away.
If one or both of these lights come on while you are
driving, pull off the road and stop carefully. You may
notice that the pedal is harder to push, or the pedal
may go closer to the floor. It may take longer to
stop. If the brake system warning light is still on,
have the vehicle towed for service. See Towing
Your Vehicle on page 182. See "Hydraulic Brake
Systems" under Braking on page 152 for further
information.
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