Make sure you get the pre-cats sensors. You need to rent/get O2 sensors socket to do the job.
Bank 2 Sensor 1 is the one on the header for cylinder 4-6. 2nd the recommendation to replace both pre-cats O2 sensors.

__________________

00 E39 DINAN S1 //M5 (82k miles)
06 E53 DINAN 4.8iS, born 2/18/2006 (126k miles) http://www.xoutpost.com/bmw-sav-foru...s-my-dslr.html
90 Straman Z32 TwinTurbo Convertible, (1 of 44 ever made) 5 speed, 444rwhp/451rwtq
01 360 Novitec Spider F1 (26k miles)