VW Polo Brake Booster Failure Causes Hard Pedal Feel

I had a very similar issue with my 2012 VW Golf TDI last year. The brake pedal was getting increasingly harder to press, and the brake system warning light kept coming on. Having some experience with basic car maintenance, I first checked the brake fluid level, which was fine. Still, I noticed the brake pedal behavior was quite concerning, requiring much more force than usual. My workshop found that air had entered the brake system due to incorrect bleeding during a previous service. They performed a complete brake system flush and proper bleeding procedure. The brake booster and pressure sensor were tested and found to be working correctly, the main issue was trapped air affecting hydraulic pressure. The repair took about an hour and cost 90€ including fresh brake fluid. After the fix, the brake pedal feel returned to normal and the warning light disappeared. To better assist with your case, could you share: When was your last brake service performed? Does the brake pedal feel different when the engine is off vs running? Are there any other warning lights active besides the brake system warning? Have you noticed any fluid leaks under the car? These details would help determine if your issue is similar to what I experienced or if there might be other factors involved with your brake system components.

I can confirm the last service was done at 101000km with oil change and brake fluid check. The brake pedal indeed feels harder when the engine is off compared to when running. No additional warning lights are showing on the dashboard, and I have not noticed any fluid leaks under the car. Since posting my initial question, I also checked the brake fluid level in the reservoir, it appears to be at the correct level between min and max marks. The vehicle safety inspection was completed 3 months ago with no brake-related issues noted. Looking at the brake system symptoms you described, they sound very similar to what I am experiencing. Did your workshop mention if this is a common issue with VW models, particularly regarding the brake pedal behavior?

Thanks for providing those additional details about your Polo. Your symptoms do sound nearly identical to what I experienced with my Golf TDI. Based on my experience, the brake pedal behavior difference between engine off versus running is a key indicator. While my workshop confirmed the brake booster pressure sensor was fine in my case, they mentioned these symptoms often point to potential brake booster issues in VW models. The diagnostic tools they used showed the brake system was not maintaining proper vacuum assistance, despite the pressure sensor readings being normal. In my case, the air in the system was the culprit, but they explained that similar symptoms can also stem from: 1. A vacuum leak in the brake booster 2. A partially blocked brake fluid line 3. A failing check valve in the brake booster Since your fluid level is good and the timing aligns with a recent service, I strongly suspect your issue might also be related to trapped air, just like mine was. The ABS system can sometimes mask these problems initially, making them progressively noticeable over time. One thing I learned from my experience: while a basic safety inspection can miss these issues, a proper brake system diagnostic test will quickly identify the root cause. The repair cost should be similar to what I paid if its air in the system, though brake booster replacement would be significantly more if needed.

Thank you for sharing those details about your brake system symptoms. The parallels between your case and mine are quite striking. Given the timing after my last service and the identical brake pedal behavior between engine on/off states, I am more confident now about the potential cause. I will have my workshop perform a complete brake system diagnostic test to check for trapped air and verify the brake booster functionality. The absence of fluid leaks and proper fluid levels in my case, just like in yours, suggests this might be a straightforward fix rather than a major component failure. I will make sure to specifically ask them to: Test the brake booster pressure sensor, Check for vacuum leaks, Verify the brake system is properly bled, Inspect all brake system components I appreciate you sharing your repair experience and costs. It helps set realistic expectations for the upcoming workshop visit. I will update once I get the issue resolved to help others who might face similar brake performance problems with their vehicles.