RS3 Brake Pedal Issues: Low Fluid May Signal Problems

Had a similar brake pedal issue on my 2013 RS4. With some car repair experience, I can share what worked for me. The spongy brake pedal and low fluid pointed to a hydraulic brakes problem. My workshop did a complete brake inspection and found worn brake pads plus a small leak in the brake lines causing fluid loss. The repair included: Replacing brake pads and rotors, Fixing the leaking brake line, Bleeding the brake system, Topping up brake fluid, Testing the master cylinder Total came to 480 Euro and solved the spongy pedal completely. Car brakes now feel firm and reliable again. Before suggesting specific fixes, could you share: Current mileage? When was your last brake service? Any unusual sounds when braking? Does the pedal sink to the floor or just feel soft? Have you noticed any fluid spots under the car? These details would help determine if your issue matches what I experienced or might be something different.

Last service was around 19128 KM. The pedal does sink almost to the floor before engaging and there is definitely fluid spotting under the right front wheel when parked overnight. No unusual sounds when braking, but the warning light just came on yesterday. The brake fluid loss and pedal behavior seems very similar to your experience. Will get it checked right away based on those repair costs and symptoms you described. Not worth risking brake failure by waiting. Related question: Did you notice the master cylinder warning light before finding the leak in your case?

Thanks for those extra details. Yes, actually I did see the warning light in my RS4 about 2 days before discovering the brake line leak, similar to what you're describing. The fluid spots under the right front wheel and the pedal sinking are classic signs of a brake system leak, matching exactly what happened with my car. The warning light typically activates when the brake fluid drops below a certain level in the master cylinder. Important: Since you're seeing fluid spots, I would strongly advise against driving the car. When I had this issue, my mechanic explained that continuing to drive with an active brake fluid leak can lead to complete brake failure and air entering the system. The repair costs I shared earlier (480 Euro) included fixing a single brake line leak. However, based on your symptoms being so similar to mine, you might be looking at comparable costs, assuming the master cylinder itself is still functioning properly. One key difference is that my leak was caught before any air entered the brake system. If air has gotten into yours (indicated by the pedal sinking to the floor), the repair shop might need to perform a more thorough brake system flush and bleed, which could affect the final cost.

The symptoms you're describing match my situation very well, especially with the warning light appearing after noticing the problem. That helps confirm it's likely a brake line leak rather than a failing master cylinder. The fluid spots by the right front wheel match the exact location where my leak was found too. Really appreciate you sharing the repair details and costs. I will have the car towed to avoid any safety risks from the failing brake system. The sinking brake pedal definitely has me concerned about air in the lines, so I will budget for a complete system bleed along with the brake line repair. Will update the forum once I get the final diagnosis, but based on the matching symptoms and warning light timing, I suspect your experience will prove to be a good guide for what repairs I am facing. Thanks for helping me understand what to expect with the brake system repairs.