i got a diagnostic test on my 95 nissan maxima and read codes: P0130 o2 sensor B1S1 and P0150 o2 sensor B2S1. Are these 2 o2 sensors indicating before or after the catalyic converter? I went to autozone for this question and they were not sure. I forgot to ask the mechanic who did the diagnostic test since my car falls under ODB-1 readings. Also, does B mean bank 1 & 2, what does S mean?