Thank you for this very helpful post. I am a little confused about bank 1 sensor 1 versus bank 1 sensor 2. I have attached a photo from my C300, from the top. I was wondering if you could help me figure out. The two images on the top are from back of the engine, and the three in the bottom is from the left side of the engine passenger side. I was not sure which one is sensor 1 of the bank 1.  Thank you again.



Sensor 1 is before catalytic converter. Sensor 2 after catalytic converter. 

Bank 2 is driver side cat bank 1 is passenger side cat. 

Cars with only one cat typically on 4 cylinders will only have bank 1.

You can verify by unpluging the suspecting sensor and read the trouble codes with an obd2 scanner. It will give you a code for oxygen sensor bank x sensor x.

karkh, 2019-02-25

Thank you for your help. Can you please look at my photo as well. Because my engine is there, so I want to make sure I am replacing the right sensor. The code for me is P0130 which refers to sensor 1 bank 1. The code is already there even without unplugging the socket. My question is from my photo is it the one on the top row of my image or the one one the bottom row of my image. Both are from the passenger side.

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