well I had this code for awhile p0431 bank 2 below threshold. Dealer told me I needed new cats 2999 each. So I decided to first change the o2 sensor. Well I tried, I could barely fit my hands and tools to get it out, I was getting terrible gas milage and loss of power, so I bought an universal o2 sensor after 3 hours I gave up so I cut the wires of the old one and left it in the exhaust. Connected the new one to the wires that I cut, put o2 simulators and left it hanging, with the old one disconnected but still in the exhaust. Filled up the car with premium and so far I'm getting 5 more miles per gallon. No CEL on or nothing yet.

 

now I got another CEL p0139, now is the rear drivers side. Low response but I think is because I left the back passenger disconnected, but gas milage still good. Huge improvement.