Hummer 2003 H2 Owner's Manual page 167

United States
This light should come on briefly when you turn the
ignition key to RUN. If it doesn't come on then,
have it fixed so it will be ready to warn you if there's
a problem.
If the light comes 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 light is still on, have the
vehicle towed for service. See "Towing Your Vehicle" in
the Index.
Your brake system may not be working properly
if the brake system warning light is on. Driving
with the brake system warning light on can lead
Canada
to an accident. If the light is still on after you've
pulled off the road and stopped carefully, have
the vehicle towed for service.
CAUTION:
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