Addressing some common misnomers of the P0420 code

Noticed that I do have a pinhole leak just after the down stream o2 sensor. Almost directly below it. Could this cause 0420? Or are leaks after the last sensor irrelevant??

 

I have a 2001 Tacoma 3.4 v6 with the P0420 and P0505 code. Have replaced all vacuum lines and did a top pan and plenum gasket replacement. Tested both o2 sensors with my scan tool o2 sensor bank 1 sensor 1 has a voltage of 3.2v to 3.3v, while o2 sensor bank 2 sensor 1 fluctuates from 0.6v to 0.06v never constant. Need help gas mileage is 10mpg to 12mpg combined.

Have also replaced mass air flow sensor, throttle position sensor, cleaned throttle body and replaced iac valve, replaced spark plugs, wires and coils.

My idle is at 1050 when cold, 1250 when hot and 860 when in drive or reverse

I keep seeing o2s inc and evap inc on the I AM readiness

Need help

 

I had to take off my throttle body and clean out my IAC. also replaced the throttle position sensor and evap purge solenoid. Had been chasing a high idle since I replaced my fuel tank. Also had a bad pcv valve oiling up the inside of my intake and throttle body, I have a PO420 because I’m catless and it doesn’t change how the truck drives so you probably just have a bad cat, or downstream o2 is funky

 

Thank you for the suggestions! I appreciate it. I've already cleaned the IAC, replaced the throttle position sensor, and ensured my vacuum lines are good. I will also replace the PCV valve and purge solenoid, as well as the fuel filter and coolant temperature sensor since I have those parts on hand, to see if there's a difference.

Currently awaiting a new downstream os sensor from denso

 

Yeah the PCV was causing a slight misfire at idle for me and the throttle position sensor was sticking keeping m butterfly valve open just slightly

 

I have replaced the front O2 sensor but the rear is VERY difficult for someone laying under the truck to do because of the heat shield is there a way to get the shield off without a lift? Mines also an 02

 

It’s doable just a bit more finicky.