For a while now, in my 2016 A200, I've been getting a pre-safe fault warning, and many of my features (steering wheel auto-retraction, ESP, auto-hold, cruise control...) would go off while the warning was on. At first, turning the car off and on would fix it, it wouldn't come back. This year, partly due to the very hot weather (you'll understand shortly), the fault came back again while I was on vacation on the island (Gökçeada), and no matter how many times I turned it off and on or whatever I tried, it wouldn't go away (daytime temperatures on the island were exceeding 40 degrees). The island roads are generally winding, calm, enjoyable mountain roads — even though there's nothing extra on my car, anyone who has driven them will understand what I mean. When you get an A200 with the AMG package (especially 2016 and later facelift), it comes with a really meaty, communicative steering wheel, seats that hug your body even if they're not real bucket seats, lowered and stiffened AMG suspension, and AMG brakes. So in short, it's quite an enjoyable car to drive on these roads, but because of the pre-safe fault, all the steering feel and feedback disappeared, and I was left with a quite dangerous, joyless, and broken steering feel. Hoping there might be an easy solution, I started researching — on foreign forums I saw that the source of the fault can come from very different things, but generally, in the cars of people who experienced this while the car's warranty was still active, the unit behind the steering wheel that also houses the turn signal and gear stalk was replaced, and less often, the ESP module or similar modules were replaced. While looking into what's inside this box, I learned that the SAS (steering angle sensor) module is located here, and with that I continued my vacation, got used to driving the car this way, and finished the trip. While driving, the fault started going away on its own at night, but it would come back again during the day, so I started to become sure the problem was related to the heat. +
Translated from TurkishReplies
7 repliesOn the way back to Ankara I had to drive like this again, and I realized the hardest thing meanwhile was living without hold assist — you really see how useful it is once you're used to it and it's gone. When I got back it was time to call the mechanics, because apart from small things I'd never dealt with my car myself, and I felt ashamed of myself as an engineer :D. I explain the problem to the mechanics and either they have no idea, or they give a ridiculous price range — some start at 15,000 lira, some say they'll do it for 5,000 lira. +
Translated from TurkishI said let me hook the car up to an OBD reader, at least to get a clearer idea of what the problem was, and what I'd been thinking about from the start was the SAS — the steering angle sensor. In modern cars, especially Mercedes, it's a part that many other control units in the car's brain get sensor data from, and when this part fails or sends out-of-range data, it causes many features like the steering self-centering, ESP, cruise control etc. to stop working and throw faults. +
Translated from TurkishAfter saying to myself 'I wish I'd researched this from the start,' I found a video by an Arab mechanic who was repairing the part, but the steps were always cut and not shown. After digging around a bit more, I saw that the Chinese had already solved this, documented it, and could even connect directly to the angle sensor and read the values. +
Translated from TurkishAnd one Saturday I started trying to fix my own car; I always thought the scariest part would be the airbag, but once you take the necessary precautions, I realized it's no different from taking apart and putting together Lego pieces. When I took the steering wheel apart and reached the part, the connection related to the heat issue was right there in front of me, +
Translated from TurkishThe material Mercedes uses to lubricate this sensor's gears starts to melt at high temperature and begins to contaminate the optical reader parts. With a good, careful cleaning (if you damage the optical reader or the optical disc, you'll have to buy a new part outright), your car's steering feel goes back to being like the day you got it and all the problems go away; and when you grease the gears again with a grease that has high thermal resistance, you can keep this problem from happening again. +
Translated from TurkishAfter fixing my car myself for the first time, I realized this: if you're handy and curious about such things, you don't have to be a mechanic or an engineer, and on problems like this the money you'd otherwise pay someone else can stay in your pocket — you can buy your car another tank of gas and enjoy it even more. I'd love to help friends who have this problem and want to tackle it themselves, feel free to ask whatever you want. +
Translated from TurkishFor those who can't deal with it themselves, on a weekend when I have nothing on in Ankara, I can fix your car for a price that has nothing to do with what mechanics ask for. If you started reading from here, because of the formatting you should start from the bottom. In the photos I added, you can see photos from the holiday and the grease that's the source of the problem.
Translated from Turkish