GLA Diesel Fuel Mixture Issue

That sounds frustrating. I had a similar issue with my old Audi A4. The check engine light kept popping on, and the engine would occasionally stall at idle. Have you tried checking for any potential fuel contamination? Sometimes bad fuel or even certain fuel additives can mess with the fuel system and cause an incorrect fuel mixture. Also, have you noticed any engine knock?

Thanks, that's helpful. Fuel contamination is an interesting point. I haven't specifically checked for that. How would I go about checking the fuel for contamination? And what exactly do you mean by 'engine knock'?

By fuel contamination, I mean things like water or debris in the fuel tank. You might be able to visually inspect a fuel sample, but it's usually best left to a professional. Engine knock is a rattling or pinging sound coming from the engine, often caused by improper combustion. Since your error memory is storing a fault related to the fuel composition and you are experiencing stalling, it is best to take your Mercedes to a workshop for diagnostics. It sounds like your issue could be related to a defective cable or plug connection, as you mentioned, and they can properly diagnose and repair that. Could save you time and potential further damage.

Thanks for the advice. I took it to a mechanic, and you were right – it was a defective plug connection. They replaced it, and the error is gone. Total cost was 95€. Appreciate the help!