[Erik-AA]

M 2010 128i is throwing repeated oxygen sensor codes. Not surprising at over 130k miles. To my surprise there is no guide to this that I can find in the forum.

I'll take photos and make a DIY guide if there isn't already one. But before I dive into it can anybody help me out a bit? I can't tell from the online info and the parts vendors whether the car has 2 or 3 or 4 sensors? Upstream for 1-3 and another upstream for 4-6? One or two downstream? I saw something about this being a big job on 135i, involving removing steering rack etc. Is that so for 128i too?

I'm inclined to replace them all while I'm in there since I'm in the right mileage range for them to fail and they're not that expensive. But the codes I'm getting are for downstream (after the cat) sensors and if the upstream sensors are a lot harder to get to I might leave them for now.

Thanks in advance for any advice!