Please explain where and how to replace. Thanks to all.

thanks for the help!

I have a 95 C220. I would imagine they are the same. The oxygen sensor is located on the exhaust pipe coming from the header on the passenger side of the car. You can see a gray wire coming up from it. Since the suspension hides it from below and the manifold hides from above, it is not visible. I have never replaced one on my car. I have replaced them on other cars that are more accessible. You need a large open end or box wrench if you can feed the wire through it. Since it is a large hex fitting you need quite a bit of torque to unseat it and not alot of room to swing the wrench. Let me know how you make out since I will eventually have to replace mine. See my post near yours. Have you ever replaced plugs on the car?

Oops, I may have steered you wrong. There may be two sensors. There is also a sensor located on the twin catalytic converter underneath the car between the two halfs of the catalytic converter. Try doing a search on this subject. I believe I saw a post on it but I can't find it right away. The second one is probably the feed back sensor. The one you want to replace.