Audi S6 Brake Pedal Issues Point to Fluid System Fault

Had a similar issue with my 2015 Audi S4 last year. Have some experience maintaining cars and initially thought it was just low brake fluid. The spongy brake pedal and low fluid level often indicates a bigger problem with the hydraulic brakes. In my case, the brake pads were severely worn, which allowed air to enter the brake system. The workshop did a complete inspection and found that both the pads and rotors needed replacement. The diagnostic process included: Brake fluid level check, Full brake system pressure test, Inspection of brake components, Test drive to verify pedal feel Total repair cost was 480 Euro including parts and labor. The car brakes now feel firm and responsive again. To provide more specific advice about your S6: When was your last brake service? Are you noticing any grinding sounds? Does the pedal sink gradually or is it immediate? Have you checked for visible brake fluid leaks? These details would help determine if you're facing the same issue I had.

Thanks for sharing your experience. My last inspection was at 125000 KM, about 6000 KM ago. The brake pedal starts firm but gradually sinks to the floor. No grinding sounds yet, but I did spot some dark stains near the brake lines on the passenger side. The fluid level keeps dropping despite recent top-ups. After reading your post, I checked underneath more carefully and noticed the leak seems worse after longer drives. Thinking it might be best to get the brake lines inspected before it becomes a bigger safety issue. Would rather catch this early, especially since the hydraulic brakes seem compromised. The brake warning light still hasnt activated, but these symptoms sound serious enough for immediate attention.

Thanks for the additional details. Your symptoms are quite different from what I experienced, and the leak you described is a serious red flag. While my issue was related to worn brake pads, yours points clearly to a brake line failure. The fluid loss and gradually sinking pedal, combined with visible leaks near the brake lines, indicates a breach in the hydraulic brake system. Stop driving the car immediately. Unlike my pad wear issue, a compromised brake line can lead to complete brake failure. The brake warning light may not trigger until significant fluid loss occurs, but the symptoms you describe warrant immediate professional attention. Your brake lines might be corroding, which is a common issue in our Audi models around the 120000-130000 KM mark. When my mechanic performed the brake service, he actually pointed out early signs of brake line wear, though mine hadnt started leaking yet. The fix will likely involve: Complete brake system inspection, Brake line replacement, Brake fluid replacement, System bleeding to remove air, Pressure testing Expect repair costs around 350-600 Euro depending on how many brake lines need replacement. This is different from my pad replacement case, but addressing it now will prevent more expensive repairs later.

Based on your input and details about the leaking brake lines, I'll get it to the shop right away. The gradual pedal sink and constant fluid loss are too risky to ignore, especially after hearing about the potential for complete brake failure. The brake warning light not activating definitely gave me false confidence, but those stains near the brake lines and the worsening leak during longer drives make it clear this needs immediate attention. The master cylinder might still be fine, but those brake lines are definitely compromised. Will schedule an appointment for tomorrow and avoid driving until then. Better to spend 600 Euro now than risk the entire hydraulic brake system failing. Really appreciate the detailed breakdown of what to expect during the repair process. Good call on mentioning the common timing of brake line issues around my mileage, makes sense why its happening now. Will update once I get the official diagnosis, but sounds like your assessment of corroded brake lines is probably spot on.