Failing RS5 Brake Booster Causing ABS System Issues

Having dealt with similar brake system issues on a 2014 RS7 (some experience with high performance vehicles), I can relate to your brake performance concerns. The symptoms you describe match what I encountered. In my case, the hydraulic brakes were not performing correctly due to improper bleeding of the brake system. The workshop found air bubbles in the brake lines which caused inconsistent brake pedal feel and triggered ABS-related error codes. The fix involved: 1. Complete system diagnostics 2. Professional brake bleeding 3. Brake fluid replacement 4. Sensor calibration Total cost was 90 Euro for the service, which solved both the brake performance issues and cleared the error codes. To provide more specific guidance for your case, could you share: Current brake pedal feel (soft, hard, pulsating)? Does the vehicle safety warning appear during specific conditions? Have you noticed any changes in brake fluid level? When was the last brake fluid change performed? These details would help determine if your issue matches what I experienced or if it points to a different root cause. Remember that proper brake system maintenance is crucial for vehicle safety, especially in high-performance vehicles like the RS models.

Thanks for the response. Just had my latest service at 57000 KM where they changed the brake fluid. The brake pedal feels increasingly soft and spongy now, getting worse over the past week. The warning appears out of nowhere, not tied to specific conditions. The brake booster pressure sensor replacement seems like a logical fix, but before booking a repair appointment, I want to confirm if the symptoms match what others experienced. The service manual mentions a complete brake system inspection might be needed along with any pressure sensor replacement parts. Looking for verification if this diagnosis makes sense before proceeding with repairs.

Based on your recent service history and the symptoms you describe, I dont think your issue matches my experience with brake system problems. In my RS7 case, the spongy pedal feel appeared immediately after service, while yours developed gradually over time. This progressive deterioration suggests a different root cause than air in the lines. Looking back at my repair process and subsequent research, a failing brake booster pressure sensor typically causes hard pedal feel rather than the soft, spongy sensation youre experiencing. When my car had a similar warning later on, diagnostic tools revealed the brake booster itself was starting to fail, which created symptoms more aligned with what youre describing. The ABS system can also trigger similar warnings when the brake booster isnt providing proper assistance. A thorough inspection of the entire brake assembly would be wise, as replacing just the pressure sensor might not address the underlying issue. If the symptoms match my second experience, you might need: Complete brake booster inspection, System pressure testing, Brake booster replacement if necessary, Recalibration of sensors The repair cost will vary based on needed parts, but budget for more than just a sensor replacement. My brake booster replacement ended up around 800 Euro including labor.

Just had the car in for a thorough inspection based on the feedback received. The brake booster was indeed failing, which explains why the hydraulic brakes were performing poorly. The brake pedal feel kept getting worse because the booster was gradually losing pressure. The inspection revealed the entire brake booster assembly needs replacement, not just the pressure sensor as I initially thought. The mechanic confirmed this matches the progressive deterioration of brake performance I experienced. While this means a more expensive repair than hoped, at least the diagnosis makes sense now. Replacement parts have been ordered and the full repair is scheduled. They will also recalibrate the entire ABS system after installation to ensure proper vehicle safety. The estimated cost is around 900 Euro which seems in line with what others paid for similar repairs. Thanks for helping point me in the right direction with the brake booster inspection suggestion rather than just focusing on the sensor. Will update once the repairs are complete to confirm if this resolves both the performance issues and warning messages.