what do the back o2 do? my check eng light is on ..says both back o2 and knock sensors.... i think my cats are geting plug up ... could that be my problem? if so can i just cut them out and put pipe back in..with out messing up the performace and my mpg ? i know my light with stay on if i do this ...

 

pretty sure the only thing REAR o2 sensors do is make sure your cats work. thats there only job

 

To control emissions of Hydrocarbons (HC) , Carbon Monoxide (CO) , and Oxides of Nitrogen (NOx)

The front HO2S sensors produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the cats The rear HO2S sensors produces an output signal which indicates the oxygen storage capacity of the cats this in turn indicates the catalysts ability to convert exhaust gases efficiently. With that said the rear sensors play a limited role in the fuel control so if you took them out no real biggie,