Mercedes Washer Fluid Warning and Repair

I had a similar issue with my old Volvo. The warning light was on, washer fluid level was fine, and the windshield cleaning system was dead. In my case, the problem wasn't the level sensor itself, although that's a possibility for you. It turned out to be a clogged filter at the bottom of the washer fluid reservoir. Have you checked that? Sometimes debris can build up and prevent the pump from drawing fluid, even if the level is sufficient.

A clogged filter is interesting. I haven't looked at that. Where exactly is that filter located within the windshield washer system?

On my Volvo, the filter was integrated with the pump at the bottom of the reservoir. You typically have to remove the pump assembly to access it. I am not sure where it is on a Mercedes, but it's likely in a similar location. Check the pump. Given the age of your car, it's plausible that debris has accumulated. You could probably clean it yourself, but honestly, at this point, I'd consider taking it to a workshop. They can diagnose it properly and might have a better way to flush the entire wiper system. I initially tried to fix it myself, but ended up creating a bigger mess. Take it to a professional.

Thanks for the advice. I took it to the workshop. The problem was indeed a faulty windshield washer pump. Cost me 25€ to replace. The windshield cleaning works again.