SQ5 Brake Booster Sensor Failure Alert and Fix Guide

I had a very similar issue with my 2016 S4 last winter. Having some experience with brake system repairs, I can share what worked for me. The symptoms you describe match what I experienced, warning lights and poor brake response. After using diagnostic tools, my mechanic discovered the hydraulic brakes needed proper bleeding. The ABS system was getting false readings from trapped air, triggering the pressure sensor warnings. The fix was relatively straightforward. The workshop did a complete brake fluid flush and proper system bleeding. The entire process took about 2 hours and cost 90 Euro. No replacement parts were needed in my case, just proper bleeding procedure. Before suggesting specific solutions for your SQ5, could you share: Are you getting any specific error codes? Does the brake pedal feel different (spongy, hard, or inconsistent)? When did these symptoms first appear? Have you had any recent brake work done? This would help determine if your issue is similar to what I experienced or if you might be dealing with a different brake system problem.

Thanks for all the extra info. My SQ5 is showing P0627 and occasional P0629 error codes when scanned. The brake pedal has developed a spongy feel over the past week and requires more pressure than usual. This all started after hitting 174784 KM, about 2 weeks after my routine oil service. The ABS system light also flashes intermittently during regular driving. The brake fluid level appears normal but I notice the brake system behaves worse after driving in heavy traffic with frequent stops. These symptoms seem different from what you experienced. Since the diagnostic tools point to the pressure sensor, I am wondering if others faced similar issues requiring sensor replacement rather than just a fluid flush.

Thanks for those additional details. Yes, my S4 case was indeed different from what youre describing. Those specific error codes, combined with the timing and symptoms after heavy traffic use, strongly suggest a failing brake booster pressure sensor rather than just trapped air in the hydraulic brakes like in my case. After dealing with various brake performance issues, Ive learned these sensors typically start acting up around the 150000-180000 KM mark. When they fail, they often trigger exactly those error codes you mentioned and create that spongy pedal feel, especially after repeated brake use. The intermittent ABS light is another clear indicator differentiating your case from my previous fluid issue. While diagnostic tools can help identify the problem, this combination of symptoms really points to sensor replacement being necessary. My suggestion would be to skip the fluid flush for now and go straight for the pressure sensor replacement. Based on my repair experience, its about a 3-hour job and the replacement parts typically cost between 180-250 Euro, depending on the sensor brand chosen. If you plan to tackle this yourself, make sure to clear the error codes after installing the new sensor, as the brake system needs to relearn its baseline readings.

Based on your thorough feedback, I understand this is more serious than just a brake fluid issue. Those error codes and the specific symptoms with the brake pedal definitely point toward the pressure sensor. The fact that its acting up after heavy traffic use makes a lot of sense now. The ABS system warnings and brake performance issues are really concerning, so I think Ill have to get this fixed properly at a workshop. A 3-hour job at around 200 Euro for the replacement parts isnt as bad as I feared. Better to address this properly now than risk further brake system problems. Going to book it in next week and specifically request they replace the brake booster pressure sensor. Good to know about clearing those error codes too, Ill make sure they do a full system reset after installing the new sensor. Really appreciate the detailed explanation. Helps a lot to understand exactly what Im dealing with rather than going in blind. At least now I know what to expect with the repair process and can make sure they address the actual problem rather than just doing an unnecessary fluid flush.