Brake Booster Issue on M Klasse W164

I understand your concern regarding the brake booster issue on your M Klasse. I own the same model and had a similar experience some time ago. The symptoms you describe, including the error message and reduced braking efficiency, align with what I encountered. In my case, the problem was indeed related to the brake booster system. May I inquire if you have recently had any maintenance performed on your brake system?

Actually, yeah, about a month ago I had the brake lines flushed and new fluid put in. Now that I think about it, the problems started cropping up not long after. What exactly was the issue with yours? Was it the sensor itself or something else? And what was the fix? This is making me nuts...

The brake lines being flushed recently certainly gives a clue to the origin of the problem. It is highly probable that there is a connection to the brake bleeding procedure. In my experience, the problem was diagnosed at a certified workshop, where they pinpointed the pressure sensor as the faulty component after carrying out diagnostic tests. I would recommend that you have the vehicle checked by a qualified technician. They will be able to determine whether the incorrect bleeding procedure has caused further damage. It is crucial to deal with this promptly, as it affects vehicle safety.

Just wanted to say thanks again for the input. Turns out you were spot on about the brake bleeding! Took it to a mechanic, and they confirmed the booster pressure sensor was shot because of air in the system. They re-bled the brakes properly and replaced the sensor. Cost me about 90€ for the replacement parts and labor. Brakes are back to normal now. Huge relief!