BMW M3 Brake Booster Sensor Issues & Repair Costs

I can relate to this issue. Had a similar problem with my 2011 BMW M5 last year. The symptoms you're describing match what I experienced, weak brake pedal, warning lights, and that distinct hydraulic pump noise. When I took it to the garage, they found that the brake system was incorrectly bled, which led to air pockets in the lines. The pressure sensor was giving false readings because of this trapped air. The fix required a complete professional brake system flush and proper bleeding using the correct diagnostic equipment. This is actually quite serious, you really don't want to mess around with brake issues. In my case, they had to use a specialized BMW diagnostic tool to properly bleed the ABS module and get all the air out. It ended up being more complex than a regular brake fluid flush. I'd suggest finding a shop that specifically knows BMW brake systems, preferably with factory diagnostic equipment. This isn't something you want a general mechanic guessing at, especially given the safety implications.

Hey, thanks so much for sharing your experience! That's really helpful to know about the air in the brake lines, sounds exactly like what I'm dealing with. Would you mind telling me how much the whole repair set you back? Also curious if you've had any other brake-related problems pop up since getting it fixed? Good to hear from someone who's been through the same headache with these finicky brake systems.

Hey there! Happy to give you an update since my last post. I got my M5's brake issues sorted out and it cost me 90€ total, which was actually pretty reasonable considering the specialized work involved. The mechanic confirmed it was indeed the brake booster pressure sensor that was acting up, and theyaged to fix it along with properly bleeding the system. Since getting it fixed, my brakes have been working perfectly, no more warning lights, weird noises, or that scary soft pedal feel. It's been about a year now and I haven't had a single brake-related issue pop up. The hydraulic pump is nice and quiet now too. Honestly, I'm just relieved I found someone who knew what they were doing. These BMW brake systems can be tricky, but once they're properly sorted, they work like a charm. Sounds like you've got the same issue I had, so hopefully this gives you a good idea of what to expect cost-wise. Let us know how it goes after you get it fixed!

Thanks for all the details! Just got back from the mechanic today actually. Turned out my situation was a bit different, had a faulty brake servo and some corroded lines that needed replacing. Ended up being pricier than I expected, but at least it's fixed now. The mechanic I found was really thorough, showed me all the worn parts, and explained everything step by step. The funny part was when they were test driving it, the mechanic's face lit up when he hit the brakes for the first time! Said he rarely gets to work on M3s. But yeah, brakes are solid now, no more warning lights or weird noises. Feel much safer driving it. The whole experience wasn't nearly as bad as my last mechanic disaster. Guess sometimes you need a bad experience to appreciate a good one! Thanks again for your help. It really gave me a better idea of what to look out for, and I felt more confident talking to the mechanic about the issues. Time to enjoy my properly working brakes!