GMC Yukon XL Denali 2005 Owner's Manual page 177

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 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 on
page 4-50.
Canada
CAUTION:
{
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
to an accident. If the light is still on after you
have pulled off the road and stopped carefully,
have the vehicle towed for service.
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