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