Find # 1 plug-- that bank is #1 follow the exhaust pipe past the converter(the converter is just B-4 the muffler) THIS is #2 O2 sensor. They use this for comparing the oxy, content drop from the first one (#1 which is closer to the exhaust manafold), THEY say that #2 O2 sensor will not trip a code BUT IT WILL READ on a scan tool as slow, it operates in much cooler temps.. If you are getting a DTC it's from the #1. If you live where they require emission testing it(#2) COULD be slow enough TO affect the reading. IF #1 O2 is not working a spec. it might tell the computer to dump more fuel and heat up the convertor causing
# 2 to read out of spec. They all work together for optimum fuel/air ratio which is preprogramed into the on-board EMC.and if it can't hold the spec to a certain % it will trip a DTC.Vacuum leaks,dirty injecters, low fuel pressure,maf,dirty filter, miss firing plugs all contribute to the mess.Start with the cheapest and work your way up/down.