I have 2001 E320 and the car started driving on just the 1st gear, no up-shift so these are the steps I have to perform to try to correct the problem:

1. Change the conductor plate - Result: Still, the car cannot shift.
2. Replaced the transmission - Result: Still, the car cannot shift.
3. Replaced the Shifter - The problem still remains.

The question is: What could be the problem?

 

If this is a W210 like my 1999 the transmission is connected to a module atop the right fender/wheel you can see when the hood is open. The connecting cable carries transmission fluid and an electric wire, inside the connector I believe. Why it was designed this way? No idea. I think this module is pretty critical to proper transmission shifting.