After Reducing R/LDo Not Press is a critical safety instruction for your vehicle’s braking system. This warning specifically pertains to the brake caliper’s internal piston during pad replacement or maintenance. The "R/L" denotes the specific caliper (Right or Left) that has had its piston retracted or "reduced" back into the caliper housing to accommodate the new, thicker brake pads.

Once the piston on the identified caliper has been successfully reset, it is imperative that you do not press the brake pedal until the installation is fully complete. Depressing the pedal at this stage will forcefully eject the piston from the caliper bore, potentially causing severe injury, damage to the piston boot, or misalignment of the new brake pads. This action can also lead to a dangerous spillage of brake fluid from the master cylinder reservoir.

To ensure a safe and correct installation, follow this procedure strictly. After reducing the piston on the specified side, immediately install the new brake pads and reassemble the caliper over the rotor. Only after both calipers (if servicing both sides) are fully secured with all hardware tightened to the manufacturer’s specification should you carefully press the brake pedal. This first press will move the piston into proper contact with the pad. You must then pump the pedal repeatedly until firm pedal pressure is restored before attempting to move the vehicle. Adhering to the "Do Not Press" rule is essential for personal safety and the integrity of your braking system.