When dealing with fuel mangement controlls, you can get over your head quickly.
The oxygen sensor is located under the vehicle about half way down on the exhaust. It is located where the transmissin and the driveshaft meet.
You could just replace it, but it may be hard to get to. You may need to have the fuel mixture adjusted when done.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS