You could repeat the test with the Engine Cold.

However, if it was working normal the Code would not come on.

I don't know enough to help and the Online Manual I have access to does not cover your year and Model.
A few People have said that you can access some of the Mercedes Manuals on Startek but I believe you need to register with them to access the Manuals.

__________________
84 300D, 82 Volvo 244Gl Diesel