SM3 Brake Booster Pressure Sensor Failure

Hello! I had a similar experience with my 2016 Opel Astra, although it wasn't exactly the same. The symptoms you describe, particularly the error message and reduced braking, are very concerning. The brake booster is essential for safe braking. Now, the pressure sensor monitors the vacuum in the brake booster – which uses engine vacuum to assist your foot when braking, reducing the effort needed to press the brake pedal. In my case the root cause was an issue with the booster itself. Have you checked your brake lines for leaks, or perhaps the vacuum hose connected to the brake booster?

Thanks for the quick reply. I checked the brake lines and vacuum hose; everything looks fine. A mechanic suggested that the brake system might have been bled incorrectly at some point and that this could have damaged the sensor. Does that sound plausible? What was the final solution in your case with the Astra?

Ah, incorrect bleeding! Yes, that can indeed cause problems, especially if air gets trapped in the ABS modulator. Air in the system would definitely affect brake performance and could potentially damage the pressure sensor over time by causing it to read incorrect values and struggle to adjust. In my situation with the Astra, the entire booster needed replacing as the diaphragm inside it had failed, so any vacuum wasn't being held and the brake pedal would be really hard to push and stopping distances were greatly increased. Given that you've checked the lines and hoses, and a mechanic suspects incorrect bleeding, I would recommend taking it to a trusted workshop. They'll be able to properly diagnose the issue using diagnostic tools and hopefully, it's 'just' the sensor that needs replacing. Stay safe!

Thanks a lot for your advice! I took it to a workshop, and it turned out that the brake system bleeding was indeed the culprit, causing the sensor to fail. The sensor was replaced, the system was re-bled correctly, and everything is back to normal. The total cost was around 90€. Appreciate the help!