Hello, I already had the problem a few weeks ago that I had received the message “Error parking brake: let vehicle repair” and “Berganfahrhilfe defective”. I got a Citroen C4 08/2012, 1.6HDI (3001/AKX) After this message the mountain starter aid really didn’t work anymore. After every restart of the engine the message went away and then came only a few time later and the mountain starter aid worked again. Since yesterday however, I get :”STOP! Error braking system: stop vehicle” It lights up the “handbraking symbol” (so an unfinished “circle” with the exclamation mark in it) In the manual it says that the brake fluid is empty. I still drove on, but now I wanted to see if there is any liquid in it at all. We have in Berlin -2 degrees and when I had turned up the cap, there was a quasi “layer” that was frozen. If I look at this from below, I see the reason and what black The brake fluid was renewed/replenished as part of a major maintenance in January 2021 (this year), braking system was also ventilated, etc. It was filled up 1 liter. I never had such a problem. I can now of course simply buy and refill DOT 4, but first I don’t think that this is good while there is dirt and second the problem is not solved. I did the inspection in January, would call there on Monday and try so fast w I’ll put some pictures on, maybe you can help me. Here are the pictures, please look at them: Thank you in advance and Merry Christmas.