Spongy Brake Pedal Points to Low Brake Fluid Issue

Had the exact same brake pedal issue on my 2020 S5 last year. Have some experience with basic maintenance, but brake system problems are best left to professionals. The warning light came on shortly after noticing the spongy brake pedal. Took it for a brake inspection right away since brakes aren't something to mess around with. The technician found worn brake pads and slightly corroded brake lines which caused a minor leak, explaining the low brake fluid level. The complete repair included: Full brake fluid replacement, New brake pads, Brake line replacement, System bleeding Total cost was 480 Euro and the brakes felt solid again afterward. The spongy pedal feel completely disappeared. Would help to know: How many miles/kilometers on your S4? When was your last brake fluid change? Are you hearing any squealing sounds when braking? Has the brake warning light appeared on your dashboard? This could be more than just low fluid, so would strongly recommend getting it checked by a qualified technician soon. Brake issues tend to get worse and more expensive if left unaddressed.

Thanks for sharing your experience. My S4 has 80941 KM and last service was done at 75000 KM with regular brake fluid inspection. No squealing sounds when using the brakes and no warning lights on the dashboard yet. However, the master cylinder reservoir is showing fluid below minimum, which aligns with the spongy brake pedal feel. Based on your feedback, I will schedule a complete brake inspection to check for potential leaks in the brake lines. Better to address this early before it develops into a bigger issue.

Good to hear back about your S4. The symptoms definitely match what I experienced, especially that spongy brake pedal feel combined with low fluid in the master cylinder reservoir. Since your last service was fairly recent at 75000 KM, and there are no warning lights or squealing noises yet, you might be catching this early. In my case, I waited a bit too long and ended up with more extensive repairs needed. The brake system should be sealed, so any fluid loss typically indicates a leak somewhere. When the shop checked my brake lines, they found the corrosion wasn't visible during regular inspections, it was only detected once they did a thorough brake system pressure test. A complete brake inspection should reveal if you have a similar brake line issue or if there might be other problems like: Worn seals in the master cylinder, Caliper leaks, Deteriorated brake hoses Getting this checked now is definitely the right call. The repair costs will likely be much lower if caught before any major component failure occurs. Would be interested to hear what they find during the inspection. This kind of brake system issue seems somewhat common on these models around the 75000-85000 KM mark.

Thanks for all the detailed info. Really helpful to know this is a common issue around my mileage range. Booked the car in for next week at my regular shop. Asked them specifically to pressure test the brake lines and inspect the master cylinder given the symptoms. They mentioned they'll do a full brake system diagnostic including checking the calipers and hoses. Hoping its just a minor leak that can be fixed without replacing too many components. Will definitely avoid driving much until then and keep an eye on that brake fluid level in the master cylinder reservoir. The spongy brake pedal feel is concerning enough that I want this resolved asap. Will update once I get the inspection results and know what repairs are needed. Fingers crossed its caught early enough to avoid the more extensive work you had done on yours.