N43 B20 120i E82 - O2 Sensor location/replacement.

[stevekoz]

Got a friend with the above car/engine combination.

Keeps getting misfires and rough running intermittently. Code reader indicates an 02 failure. The post-cat sensor has just recently been replaced but this is a code for the bank 2, sensor 1. Does the 4 cylinder have 3 x o2 sensors like the 6cylinder? Ie bank 1 sensor 1, bank 2 sensor 1 and post cat? Just want to know if i'll struggle swapping it out for them and if so which one is which, i just have 2 on my car so its easy to know.

I am assuming bank 2 sensor 1 would be the sensor further back on the left side of the engine not the one towards the front?

Thanks in advance

[preacherman]

I think there is only 1 pre-cat and 1 post-cat sensors on the 4cyl engines (plus 1 NOX sensor). The 6cyl have 2+2 (+1 NOX). I feel like I've read that the code descriptions may give red herring clues for the 4cyls but I have a 6cyl so can't say for sure.

Realoem isn't 100% clear but might help: https://www.realoem.com/bmw/enUS/showparts?id=UC12...