I would begin by having someone read the codes. If you track down Jim Forgione"s web site, he gives instructions for making a simple LED reader. I think mine cost a whopping $10.
It is easy to use so at least you have an idea where the problem is. Far better than guessing and throwing parts at it.
Also contact "S Class Eddie" in Boston. Great guy for used 140 parts.
Anziani
'97 CL600 56K