Hi all i have a rx300 with multiple emissions/fuel trim codes. Codes:
P0300 (Random/multiple cylinder misfires detected)
P0302 (cyl 2 misfire)
P0304 (cyl 4 misfire )
P0306 (cyl 6 misfire)
P0174 (system too lean, bank 2)
P0136 (o2 sensor circuit malfunction bank 1 sensor 2)

My first thought was the p0136 was the culprit, if bank 2 is lean and misfiring, why does the o2 error list bank 1 sensor 2? Sensor 2s are post cat iirc, is there only one post cat sensor and this is why? (I havent gotten under it yet will tonight) If there is only one post cat does it mean the p0136 is likely secondary to the bank 2 lean condition or seperate issue from? Since if p0136 was the cause and only 1 post cat it should be effeting both banks?

Ancedotal: In last 6mo flex pipe on exhaust has been replaced (that caused similiar codes) and one front o2 (A/F) sensor(also similiar codes dont remember exact)

 

Is it running/idling rough? I can't see the reason that's causing the misfires but if it's misfiring often then it'll definitely affect the cat and trigger the downstream O2 sensor. Also yes, there is only one O2 sensor for each of the two cats.

 

It was running slightly off until i reset codes, then ran pretty normal, i had to leave after reseting them(my mothers vehicle) and was told light came back on after 20-40miles. Ill be rechecking codes to see if all or only some came back, if theres 2 cats and 2 post cat o2 sensors it seems pretty odd to me bank 2 is having issues but the bank 1 post cat o2 sensor is in error, them being unrelated would seem odd to me as well but idk. I may just swap the bank 2 plugs and the bank 1 sensor 2 o2 sensor and see where that gets. If there is indeed seperate post cat o2 sensors for each bank i would now think the lean condition is primary cause and p0136 is seperate issue and/or unrelated?