Help me identify these sensors
 

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?

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.

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

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

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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

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

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.