That is usually a indicator that the light sensor may have failed.
It is clipped to the windshield just in front of your rear-view mirror.
Behind the plastic cover.
Was you windshield replaced recently? Glass guys can be hard on them.
DR.D

__________________
Dr.Diesel -
Shop Foreman
Master Guild Mercedes-Benz Technician.

Think the dealer is expensive? Do you know how much it costs to train a dealer tech? Or buy the required MB special tools to have on hand?