Help me identify these sensors

[nebilex]

So i used an obd reader to pull the codes on the x5 and here is what i got:
P0135 (O2 sensor circuit) P161 (O2 sensor circuit) P155 (O2 sensor circuit) and P420 (catalyst system efficiency below threshold). The latter is basically telling me i need a new catalystic convertor. My question is: what are all the other O2 sensors?

[Brandon002]

Yes, swap out your O2 sensors, reset the ECU and see if that solves it. A lot of times faulty O2 sensors can trip that catalist efficiency warning.

Chances are you do not need cats, you only need O2 sensors.

[nebilex]

Thanx Brandon, is there a way to tell which sensors these are? Front / rear bank, pre-post cat?

[puddinboo]

nebilex you do you know where they are located on the 3.0i?

[Helihover]

...

[nebilex]

Yea 2 of the O2 sensors are right on the exhaust manifold, i need to check where the other two are which i assumed they are pre-post the cat

[THE VEIN]

Change all you o2 sensors. Pre car sensors are on the exhaust manifold and post cat sensors are after the cat converter

[Brandon002]

Typically when you get the catalyst thresh hold error the pre-cat sensors have failed, causing the post cat to read incorrect.

You can start by replacing the pre-cat sensor(s) and see if that fixes it. I would replace all of them though as if the pre-cat sensor(s) go the post-cat isn't far behind.