I have a 2000 4Runner with CA emmissions and in December the CEL came on and I had P0420 code with 128K miles on it the CATS were replaced (not with OEM CATS) and all was good for 1 month then the CEL comes on again and it is the same code. I just repalced the upstream O2 sensor and now 2 days later get the same P0420 code. Will replacement of the downstream O2 sensor help or is the issue with not having OEM CATS, or do I just ignore the code?

Any help would be greatly appreciated.

 

Ignore the code.... J/K look up URD and get the O2 simulator and you wont have to worry about the down stream O2 ever again.

 

i had an emissions code show up also...it couldnt hurt to try cleaning your maf sensor...

 

I went ahead and replaced the downstream O2 sensor, it looked to be in pretty rough shape a lot worse looking than the upstream one. I had fun getting the nuts loose they were rounded off. The MAF was cleaned not too long ago as I had that code pop up as well some time back.

I cleared the code Saturday night so I will see what happens now with 2 new sensors and 2 new Cats.

 

I also have a re-occuring p0420 code.

I have found that mine will come on about a day after I fill up with garbage gas. seems to stay off if I use decent gas. it also seems to stay off longer after I installed my supercharger about a year ago.

 

Good luck passing...

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