Code P0420, who can recommend first o2 sensor to swap first?

Hello! got a check engine light, went to advance, and got the P0420 code. Looking at it, it says bank 1. I'm aware it might be the catalytic, but would like to swap the sensors first as they are much cheaper and read a lot about folks having faulty ones.

Looking at the code description on the print out attached, which of the 4 sensors does someone with experience suggest? Bank 1, sensor 1? thanks in advance.

 

I used to get this code every few months, I would go ahead and replace both, possibly your Cat also if its been on for a while. I did that and have not seen the code in 2+ years

 

I think I got some bad diagrams. My question was in regards to the fact that the diagram I had, had 4 o2 sensors. I see now that's in error. Going to post this diagram for the o2 sensors for anyone who finds this thread in the future. I see now there are only 2 sensors for the 1st gen tacoma. One upstream, one downstream, so in retrospect my question appears foolish. hope this helps someone else at some point...

 

How many miles?...swap in new sensors, but more than likely at least the front 'precat' is going bad, it is the one that takes the real pounding from the engine exhaust heat...I was getting the PO420 code, replaced the O2's, code stayed away for awhile, then came back...precat install as soon as my Rock Auto order gets here...I have 285,000 on mine, probably gonna need the second cat too, just doing it as I can afford...opinion here is the first one goes before second one...my gas mileage is still good, 20.1 average, so they aren't blocked, just wore out....I have cleaned the Maf, still throwing codeski...

Good luck, the dang nuts on the back O2 sensor can be a biatch, I found the front one to be a piece of cake...

 

ah, rad, thanks bldegle2! I think i'll get that second sensor and just swap both at the same time. and yeah, I keep reading about needing a socket that bends, and that the clips are hard to get too. Truck has just over 200k miles on it and it's in near perfect shape, having been previously owned by an older gentleman who babied and garaged it, and then also getting a brand new frame a year ago.

 

Check fuel pressure. Low fuel pressure can cause bad readings at the O2 sensors.