I want to change the O2 sensor for my 190E 2.6, but the problem is that I just got the car and I couldn't find it. Can somebody help me locate the O2 sensor???.... Thank you very much.

 

If its bad you will get a check engine light. If you do not have that leave it alone. Actually it should be in the exhaust before the cat but if you have not done it before don't do it yourself. They can be difficult to get out and you can ruin the threads, that will cause you lots of grief