I have a 99 Si with the B16. I think both of my o2 sensors are bad and bought the upstream one (before cat). I have a question though. Is there a difference between the two BESIDES one wire being in a different location? They are both 4 wire, the only difference I see is the wires are swapped. Can I buy 2 upstream and switch the wires? The price difference is huge at AutoZone etc but they are both around $250 from honda. Let me know, I can get the upstream ones (OE not universal) through a friend for $50 but the downstream are $180, if this is just a wire I will save $130 that I could use for much more interesting parts than an o2!!!!!!!