Mercedes: check engine electronics, oxygen sensors, e300d

Question
I have a 1996 e300d and my problem is that the check engine electronics light comes on stays for some time and comes back to repeat again more than one mechanic has worked on it replaced both transducers,the change over valve, the ignition switch and some that i have forgotten about even with the computer my e300d refuses to reveal its secret; Would you have any idea what it could be?

Answer
Bob,
There are many places that can cause the lite to trip on. Bad grounds, bad oxygen sensors. Automatic Break System etc etc.
Disconnect the battery terminals and leave them off for 15 minutes. reconnect  positive first then ground.
See if that resets the lite. If this vehicle has a catalytic converter  have the exhaust checked for proper gases.
Good Luck
Rob