I have been fighting the notorious P0420 and P0430 for quite a while. I changed my OEM bank 2 O2 sensors and it did get rid of the P0430 code for a few weeks but it came back…
I read another thread about an exhaust problem, asked a question or two and got a reply from @RPM WS6 who told me about a GM TSB covering bad Catalysts on the 2000-2002 LS1 F-bodies.
This got my interest again to find a cheap solution because I didn’t want to spend big $$$$ fixing it…

the solution was a $7 Spark Plug nonfouler. Yep, this really works and it doesn’t matter if the cats are there or not, according to some on YouTube.
I found my $7 defoulers at Autozone.
this will work if you have a P0420 and/or P0430…if you have other emission codes, no guarantees…and,
YOU MUST HAVE FOUR OPERATIONAL O2 SENSORS.

All you need is one package of two nonfoulers, again $7.
you will need to drill out the nonfouler to make the O2 fit but DON’T drill all the way through like many youtube videos tell you…some suggest putting steel wool in the nonfouler but I didn’t because I thought it might rust, besides, the mod worked without steel wool.

NOTE: They tell you to drill all the way and then put the other nonfouler on the first, if you do this, it will be too long and you will need a 90 degree fitting…

you want to retain the small hole on the nonfouler…again, take it slow and DON’T drill all they way through.
drill a little at a time and keep test fitting until the sensor will bolt in the nonfouler.
reassemble, clear the codes and they won’t come back…

the idea is the nonfouler has the small hole and it moves the o2 sensor away from the main stream of the exhaust gasses.
this should work on any car regardless of the exhaust configuration…
this will NOT pass a sniffer
this will pass some emission tests
this may or may not pass a visual test.

 

I need to try this. I have code p0420 on my 2001 Formula and hopefully this works. Thanks.

 

So this works and sometimes it doesn’t work just as a heads up for some people. It can also set other codes like 02 slow response codes since it restricts the reading of the 02 sensor. It’s a 50/50 shot to work trust me I know from trying this on 50 plus vehicles

 

Almost a year now and still no Check Engine Light…hope it continues.

 

Had to install some cheap aftermarket cats on my Prius and the PO420 has been on and off ever sense... might give this a try for the heck of it.
thanks for the update

 

I have a friend that did this I do suggest getting the stainless ones as steel will corrode badly ask me, Er, I mean my friend how he knows

 

Don't put them on the front 02 sensors like I've seen on a couple cars that have came into the shop. It does NOT help anything.