not sure if you worded this wrong but, the downstream O2 is a monitor only. The only function the downstream has is to monitor catalytic converter efficiency, You compare upstream / downstream readings and the difference will let you know if your cat is working or not. Downstream has absolutely zero info on how your engine is running, that is all on the upstream data, which will tell the pcm to either take away or add fuel ... then you get into long term / short term data and thats a whole days worth of schooling !!
