o2 sensor locations needed

Hi, does anyone happen to know the s answer to this P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2) refers to which oxygen sensor on a 2004 mitsubishi galant es 4 cylinder ? There are 5 o2 sensors and noone seems to know which one is the 1 I need..

i think there is a service manual here for the 9g. not sure.

universal sensor O2 - Bosch LS-07 № 0258986507 - 36Y. http://s41.radikal.ru/i093/1004/fb/962769329254.jpg Right DENSO, on the left BOSCH.