Reduced Brake Power
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, 2004 Chevrolet Cab & Chassis Silverado, and 2003 GMC Sierra. However, it is still accessible from the selected car via links, so may be relevant.
The REDUCED BRAKE POWER message is displayed when the supplemental brake assist signal circuit is held low. This happens when the SBA is active and maintaining reduced brake power levels.