GMC 2007 Sierra 1500 Pickup Owner's Manual page 278

SERVICE BRAKE BOOSTER
CAUTION:
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Your brake system may not be working
properly if the SERVICE BRAKE
BOOSTER message is displayed.
If the brake system warning light is also
on, you should have the vehicle towed for
service. See Brake System Warning Light
on page 254.
If the brake system warning light is not
on, you still have brakes, but the
supplemental brake assist system on
vehicles with rear disc brakes may not
operate properly. In the event of a vacuum
loss, you may not have vacuum power
assist for braking. The brake pedal will be
harder to push and it will take longer to
stop. If you continue to drive with this
message displayed it can lead to a crash.
Have the brake system serviced as soon
as possible.
278
If your vehicle has vacuum assist power brakes,
this message will be displayed on the DIC
when there is a problem with the Supplemental
Brake Assist system. If the message is displayed
immediately after starting the vehicle or the
message appears while driving, the Supplemental
Brake Assist system needs service. See your
dealer. See Brake System Warning Light on
page 254 for additional information.
SERVICE BRAKE SYSTEM
If there is a problem with the brake system, this
message will be displayed on the DIC. If this
message appears, stop as soon as possible and
turn off the vehicle. Restart the vehicle and
check for the message on the DIC display. If the
message is still displayed or appears again
when you begin driving, the brake system needs
service. See your dealer.