Code P0420

Hi , I am pulling my hair out trying to get rid of this code. I have recently changed all 4 o2 sensors and now I’m getting code P420 bad catalyst. Basically saying my catalytic converters are bad . Problem is they don’t seem to be there’s no smell the welds are perfect fine, I have great torque when I get on the gas, my question is if I put after market 02 sensors in my 2003 Toyota tundra 4.7v8 will this throw me this code. Should I just order new sensors? The sensors I got were kind of different then the ones that were in there will this effect the performance of the o2 sensor itself?

 

Use OEM, not aftermarket. Toyotas are pretty finicky with electronics, very sensitive to voltage differences.

 

This

you can try adding those spark plug spacers and see if that maybe a cheap fix for you.

 

Thirded.

Rules of thumb w/O2 sensors, learned painfully over and over again on this forum:

• One of a few parts you never go aftermarket with. Denso brand only, Denso is OEM. Their finder is at www.densoautoparts.com, always look up your own p/n, and know upstream is often called "air/fuel ratio sensor"
• Always buy the 'exact fit' sensor, never 'universal', more importantly NEVER cut/splice the OEM harness to install a sensor
• Replace in pairs, i.e. always do the upstream and downstream at the same time

A couple other important notes.

First off, these trucks have problems with aftermarket cats, unfortunately, that's something to pay attention to; has anyone replaced the driver cat?

Second, any leak in the exhaust system between the upstream and downstream sensor can cause also this code.

Read more on P0420/P0430 HERE.

 

Oh, and also from the FSM. Note the table "Trouble Area". There's really only 4 things that can go wrong here. Leak, bad/underperforming O2 sensor, bad/underperforming cat.

​

 

All good advices here. I would do the following too to trouble shoot.
1) install back the old O2.
2) with a scanner tool check how voltage is changing. Here you can start learning if it is an open circuit if no voltage at all.
3) if voltage is jumping out of range, install spark plug fowlers. They will bring voltage reading within reasonable range by bypassing the gases stream to the sensors.
4) if 3 solved your issue, you have bad cats.

 

Good example of #1-2 at 1m33s mark in this video.

https://www.youtube.com/watch?v=jS957rtbcjY#t=1m33s​

 

If you're trying to fix the codes for emissions testing and get a smog tech that crawls underneath and does a visual, you'll won't pass with spacers.

 

You mean you don't zip tie a $20 right next to it with a note that has a winky face?

 

Does any tech actually do that?

 

Yes. Happened to me earlier this week. Dude crawled underneath and wrote down the serial number or something else from the cat too.