RS4 Brake Booster Failure: Soft Pedal Warning Signs

Had a similar issue with my 2017 S5. The symptoms you describe match exactly what I experienced, soft pedal feel and degraded brake performance. The ABS system showed similar error codes. The root cause was incorrect bleeding of the hydraulic brakes after a routine brake fluid change. Air pockets remained in the system, causing inconsistent pressure and triggering the sensor warnings. The brake booster was actually fine, but the symptoms mimicked a booster issue. The fix required a complete system rebleed using proper diagnostic tools and following the correct sequence. Modern brake systems are sensitive and need specific bleeding procedures. The mechanic had to: Perform a full system scan, Use a pressure bleeder to remove all air, Bleed each circuit in the correct order, Reset the ABS system, Verify proper brake performance This was a serious safety issue that required immediate attention. Without proper brake pressure, emergency braking capability was compromised. The repair itself wasnt complex, but required expertise with modern ABS systems and hydraulic brake components. Suggest having a certified shop check the entire brake system, not just the booster. Replacement parts may not be needed if its just trapped air, but proper diagnosis is essential.

Thanks for sharing your experience. My brake booster issue was also resolved after proper diagnosis. Makes me feel better knowing these symptoms are somewhat common. The ABS system warnings went away completely after the fix. Did you remember roughly how much the repair ended up costing? Also curious if youve had any other brake-related problems since getting it fixed? My hydraulic brakes have been working perfectly after the repair but always good to know what to watch out for.

Since getting my S5 repaired I have had zero issues with the brake system, everything works exactly as it should. The brake pedal feel is firm and consistent, with no warning lights or error codes reappearing. The total repair cost was 90 Euro for the complete brake system rebleed. The brake booster pressure sensor was functioning correctly once the air was properly purged from the system. No replacement parts were needed since the root cause was simply trapped air from the previous incorrect bleeding procedure. The diagnostic tools confirmed the fix was successful, and the ABS module now shows no errors. Modern brake systems are quite reliable when serviced correctly, the key is finding a technician who understands the proper bleeding sequence and has the right equipment to do the job. If your brakes are working well now, just keep up with regular fluid changes using the correct procedure. A properly maintained hydraulic brake system should give you years of trouble-free service.

I finally got the brake issue resolved last week. Took it to a certified shop that specializes in performance vehicles. They immediately spotted the trapped air in the hydraulic brake system, exactly what you described. The mechanic walked me through the whole process. They used specialized diagnostic tools to scan the ABS system and found multiple pressure sensor readings were off. The brake pedal got its firmness back after they completed a proper system bleed following the factory procedure. Total cost came to 120 Euro for the diagnosis and repair. Much better than the 800 Euro quote I got from my previous mechanic who wanted to replace the entire brake booster. The braking performance is now back to normal and all warning lights are off. Really glad I asked here first and learned about the proper bleeding procedure. Could have spent way more money replacing parts that weren't actually faulty. The brake system has been working flawlessly since the repair.