Well this is really weird, I looked all over for the wiring/conectors for the two upstream sensors and found nothing, so I decided to do some research and this particular BMW shop told me my particular model has a simplier design and it only uses 2 sensors, 1 before the cat and one after. They sent me a diagram and now I am shocked because I have never seen this in any other of the BMW's I owned at some point.

This is a 1998 323is with a M52 engine in case it matters.

BMW always surprises me one way or another.

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This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: BMW 3 Series (E36) Oxygen Sensor Replacement

Looking at the wiring I see two sensors. Same with parts. I would like to look the information for your specific vehicle up. I think I remember hearing this in the past, about single o2 pre and post cat engines.

- Nick