2004 GMC Sierra 1500 Pickup Owner's Manual - Page 235

SERVICE 4 WHEEL STEER {CAUTION: 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" in the Index. If the brake system warning light isn't on, you still have brakes, but the supplemental brake assist system 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. If a problem occurs with the 4 wheel steer system, this message will appear 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 being driving, the four wheel steer system needs service. SERVICE 4WD If a problem occurs with the four wheel drive system, this message will appear 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 four wheel drive system needs service. SERVICE RIDE CONTROL If a problem occurs with the suspension system, this message will appear on the DIC. If this message appears, stop 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 air suspension system needs service. 3-71