Q3 Hybrid Brake Booster Failure: Warning Signs & Fix

Had a similar issue with my 2021 Q5 Hybrid last spring. As someone with basic car maintenance experience, I first suspected the ABS system but it turned out the brake system was incorrectly bled. The symptoms matched exactly what you describe, spongy brake pedal and warning lights. The pressure sensor was reporting errors because air bubbles were trapped in the system. My workshop did a proper brake fluid flush and complete system bleed, which cost 90 Euro and fixed the issue completely. Since your car is newer and under warranty, definitely have the dealer check it. The brake booster and pressure sensor issues often stem from improper maintenance, but could also indicate other problems. Would be helpful to know: Current mileage on your Q3, When was the last brake fluid change, Are the error messages constant or intermittent, Does the pedal feel worse when engine is cold or warm This info would help determine if your issue is similar to what I experienced or potentially something different.

Last brake fluid service was at 15000 KM during routine maintenance. Error messages appear intermittently, mainly during cold starts. The pedal feel is most spongy when the engine is cold, but improves slightly after warming up. The hydraulic brakes started acting up about 2 weeks ago. Vehicle safety is my top priority, so I want to get this resolved quickly. The brake performance definitely feels compromised compared to normal operation. Will schedule a warranty appointment soon but wanted to gather some community insights first. Thanks for sharing your experience, the trapped air theory makes sense given the symptoms and diagnostic tools readings.

Based on those details, your symptoms definitely align with what I experienced, particularly the cold-start issues and pedal behavior improving with warmth. After my brake system service, I learned these hybrid brake systems are more sensitive to air in the lines than conventional setups. The intermittent nature of your pressure sensor alerts and timing since the last fluid service strongly suggests air infiltration in the hydraulic brakes, just like my case. When mine started showing these symptoms, the brake performance was noticeably affected, especially during the first few minutes of driving. Even though the fluid was changed recently, modern hybrid brake systems can develop issues if even tiny air pockets remain after service. The pressure sensor triggers warnings because it detects inconsistent hydraulic pressure, which matches the error codes you mentioned. While my repair was straightforward, recommend having the dealer thoroughly check the entire brake system since yours is under warranty. They should: Perform complete system diagnostics, Check for any vacuum leaks, Properly bleed all brake circuits, Verify pressure sensor operation, Test brake booster function Keep documentation of the intermittent nature and cold-start correlation of the issues for your warranty claim. Worth mentioning any error codes stored in memory during your service visit.

Thanks for the detailed response about the brake system issues. Your similar experience helps confirm my suspicions about air in the lines affecting brake performance. Will definitely mention those cold-start symptoms and pressure sensor readings when I take it in. Since the diagnostic tools showed those error codes and the brake pedal continues feeling inconsistent, I scheduled a warranty appointment for next week. The service advisor noted they will do a complete inspection of the hydraulic brakes and ABS system components. Makes sense about hybrid setups being more sensitive. Just hoping it is something simple like trapped air rather than a faulty brake booster or more serious issues. Will update once I get the results from the dealer inspection and repairs under warranty. The spongy pedal and compromised brake performance are concerning enough that I want this resolved ASAP. Safety has to come first, especially with a relatively new vehicle. Appreciate all the insights from others who have dealt with similar brake system problems.