2005 Tacoma p0420 Code

I can't quite figure out what I should do.
I took it to a mechanic, and he said it would be pointless for me to dump money into fixing exhaust / o2 sensors because it would
a) cost a lot
b) no laws saying I need to meet any emission requirements.

Don't know if there's a way to bypass my o2 sensor, so it stops throwing a code or if I can test whether its the o2 sensor or the catalytic converters to see if I should replace it myself and whether I should even worry about it

 

Welcome to TW.
I had that code. Turned it to be a bad gasket where the cat meets the Y pipe.
The leak was small and I was under there more than once before I saw it.
If you're interested, get a bluetooth OBD2 scanner and the torque app. The app lets you make gauges for lots of things. I made gauges, graph style, and was watching the O2 sensors. One was smooth, the other, all over there place.
The gaskets cost about $30 and it took me a couple hours to replace.
Haven't had that issue since.

 

Rockauto has denso (OEM Manufacturer) O2 sensors. Replaced both of mine and my stutter and rough idle went away. Check the gasket when its cold (soapy water). If you dont have any leaks, most likely its the O2 sensor. Just need the code reader to find out if its upstream or downstream (I think).

 

If you have a lot of miles on your truck it could be as simple as your Cat(s) needs to be replaced.

Also, if you have a IR thermometer, check the temp upstream and down stream of the cat. If the temps upstream is 100°F or so hotter than down stream then you're cat is clogging up.

 

O.P. fix the problem,don't just ignore it like your guy told you.

 

Yeah why not fix it? Ignoring will worsen your idle and mpg. There alot of good threads in this here at TW.

I replaced Bank 1 sensor 2 after throwing a code and CEL went away. Amazon and rockauto have good prices, $50-150 depending on which sensor. Use ONLY Denso. No reason to not try to fix it. Also check for any exhaust leak. How many miles?

 

1) OP, the most important thing you need to do right away is finding another mechanic.
2) clean MAF sensor, clear code and see if it comes back
3) Buy a code reader and recheck the code and see if it states the sensor/bank location and go from there.
4) After cutting ties with the mechanic, follow up and send him this book:

 

o2 extender/spacer, cost like 8 bucks and it will make the code go away.