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I recently bought a 318ci but have had problems with the botched job done to the exhaust. The pre-cat o2 sensor (before the catalytic converter but after the downpipes merge) is there in the exhaust but has no wire coming out of it. I have ordered an OEM o2 sensor for this position and it has a 360mm long wire. With the wire not being long, I thought it'd be straight forward to find where the sensor plugs in but no. It seems that the loom has been completely cut off and so I can't install the new sensor.
The o2 sensor I'm talking about is labelled no.12 on the diagram on this link

As a result of the sensor not being plugged in anywhere, I'm getting poor fuel consumption and occasionally rough idling. The Engine Management Light also comes on. My OBDII gives the error code p0420 (Catalytic System Efficiency Below Threshold Bank 1) and I just erase the code. I'm hoping that these problems can be resolved by properly installing this sensor.

Could anyone please advise on how I can go about solving this problem or possibly share a picture or diagram which shows where this sensor is meant to be connected.
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