Spongy Brake Pedal Signals Urgent SQ5 Safety Check Needed

Had similar symptoms on my Audi S4 (2015). The spongy brake pedal and vibration often indicates air in the hydraulic brake lines or deteriorating brake fluid. After inspection, the brake calipers were found sticking, causing uneven brake pad wear and reduced braking performance. The main issue was contaminated brake fluid that had absorbed moisture over time, leading to partial system failure. This required a complete brake fluid flush, replacement of corroded brake lines, and new brake pads. The brake calipers also needed thorough cleaning and lubrication as they were partially seized. This is indeed a serious safety concern that should be addressed immediately. The metal brakes system is critical and these symptoms suggest multiple potential failure points. My case revealed that the previous mechanic had not properly bled the brake system after service, introducing air into the lines. Would strongly recommend getting a second opinion from a certified Audi specialist who can properly diagnose the hydraulic brake system. The symptoms you describe closely match what happens when brake fluid becomes contaminated or when air enters the system.

Thanks for the detailed reply. Very similar to what happened with my SQ5 last year. The brake rotors were also warped due to the sticking calipers, causing that vibration through the brake pedal. My brake pads were completely worn on one side too. Would you mind sharing what the total repair cost was for your brake system overhaul? In my case, I also ended up replacing both front brake rotors since they were beyond resurfacing specs. Still keeping an eye on the brake performance since the fix, but curious if you had any issues pop up afterwards?

After getting the Audi S4 to a certified mechanic, all brake-related issues were fully resolved. The complete brake system overhaul cost 240 Euro to get everything back to proper working condition. The brake calipers now operate smoothly without any sticking, and the metal brakes provide consistent stopping power. The contaminated brake fluid was completely flushed and replaced, restoring proper hydraulic pressure throughout the brake system. No more spongy pedal feel or concerning vibrations since the repair. The disc brakes now engage evenly on both sides, which eliminated the uneven pad wear issue. Have put about 15000km on the car since the fix with zero brake-related problems. The brake pedal response remains firm and predictable. Regular brake fluid checks show no signs of moisture contamination or deterioration. The investment in proper repairs definitely paid off in terms of safety and performance. Just make sure to stick with routine brake system maintenance going forward. Fresh brake fluid and regular caliper inspections help prevent these issues from recurring.

Thanks for the input. After visiting a certified shop, they confirmed it was similar to what you described. The brake system needed a thorough overhaul. The mechanic found contaminated brake fluid and air in the lines, just like your case. The repair bill came to 320 Euro for the complete job, they flushed the hydraulic brakes, replaced worn brake pads, and resurfaced the brake rotors. The disc brakes now feel solid again with no vibration or sponginess. Such a relief to have proper braking response back. Been driving for about 2000km since the fix and the brake system performs perfectly. No more concerning noises or pedal feedback. Definitely learned my lesson about proper brake maintenance and using qualified shops. Will be sticking to the recommended service intervals for brake fluid changes from now on.