I had the same probalm with my old E300 92 esp when the weather started to get warm i changed the overvoltage relay. some other relay too then the computer..then someone at mercedes told me that the for some reason the computer connections INSIDE the box meanin the printed circuits get loose .So i opened the first computer i had originally ,took both circuit board a part and reheated all te connections witha soldering iron..Guess what i drove that car for another 3 years and its stilll running.