Pre cat Oxygen sensor Cylinder #4-6 (98 S52 Code)

I need to find out which one this is so I can change it ASAP! I have a replacement OEM O2 sensor sitting next to me, so any help would be great.

My guess is that you've a 323 (there's no such thing as a 332) with an M52 engine. In that case the pre-cat sensor for bank 4-6 is mounted in the exhaust headers closest to the firewall. It accessible from the top of the engine.

The car is a 325i with a 98 S52 swap