My ML55 has the "check engine" light on and when I plug in my code reader, the code "P0130" "O2 sensor circuit malfunction" "bank 1" "sensor 1" appears.

I have installed a K&N air filter and cleaned the Mass Air Sensor since. No luck! Perhaps I have misunderstood which "bank" or "sensor" entirely??

I'm hoping someone out there has had some experience with diaganosing this. Thanks in advance for your help.
Aram

o2 sensor and airmass sensor are two seperate issues, it is likely the o2 sensor is slow to react and is setting a code by that slow reaction, you need to throw the k&N filter in the trash and get the original back in there, and hopefully you havent damaged the air mass sensor.

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I just replaced an O2 sensor myself thanks to the help provided by this forum; do a search and you'll find a ton of info. I believe "bank 1" is the passenger side and "sensor 1" is closest to the engine along the exhaust.

They are cheap to replace and a little contorting & 22mm crowfoot was needed for me to get mine done. Let me know if I can help more.

Thanks again to the forum regulars who provided me with the O2 sensor help!

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Francis E. Abate
Automotive Restoration & Preservation
Sheet metal, trim and upholstery

Which O2 code did you have? I have a potential failure in bank 2 sensor 2 (rear) O2, code 161 which is a heater circuit failure of the sensor that my local MB dealer replaced 15 month ago. I just cannot believe that the sensor would fail so prematurely.
Thanks.

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Well, I got under the ML and replaced the o2 sensor (bank1, sensor 1) and the light and code still read "o2 sensor malfunction." I'll drive it another couple days prior to visiting the dealer. It may just need a couple of days to recalibrate.

It took a total of 25 minutes (including lifting the ML) to replace the o2 sensor. A bit tight, but you are right, completely doable.
Thanks again.
Aram