Like a lot of people, I get a PO420 code in my '99 (5 speed). Mine happens a few hundred miles after reset.

I started checking into it, and it's for "Catalyst System Efficiency Below Threshold (Bank 1)"

After thinking about it, I decided to check the equivalent bank 2 code. That's PO430. So, I gave it the Google vote:
http://www.google.com/search?hl=en&lr=&q=4Runner+PO420
vs.
http://www.google.com/search?hl=en&lr=&q=4Runner+PO430

Almost 20 times as many responses for Bank 1 vs. Bank 2. This means to me there is obviously a defect in Bank 1, or random problems would be equal on both sides.

Has anybody checked into this???

 

All I can say to you man is join the club. There are several of us with the CEL due to the catalytic converters. I've got a thread going right above this one about it. My cure for now....use my handheld OBD2 to clear the CEL until I notice a drop in gas mileage or performance. We don't have emissions testing here in Birmingham and I'm not spewing exhaust like some of these idiots out there, so until we can all come to a consensus as to the root cause I'm going to leave it alone.

Matt

 

My local dealership replaced my cat under the emissions warranty at about 65k or 75k miles (can't remember at the moment) when I threw the bank 1 CEL.

 

Steve, your 4runner only has a Bank 1 (no Bank 2) since it only has (2) O2 sensors (as do the majority of vehilces out there). Bank 2 is reserved for vehicles with (4) O2 sensors such as many V8's and a few V6's. So that being said, I'm not sure how much info on Bank 2 for a 3rd gen will help.

You can follow Matt's thread on the same subject over here too:
https://www.yotatech.com/forums/f2/catalytic-converter-replacement-89187/

 

Here's the temperatures on the exhaust pipe that I measured this morning after driving an hour to work...

Before 1st O2 sensor--445
Before 1st Cat--395
Between Cats (Right before the 2nd one)--285
After 2nd Cat--265
After 2nd O2 Sensor--295

I double checked the reading after the 2nd O2 sensor, and it continually read higher than the outlet of the 2nd cat. I don't understand this. These numbers mean anything to you guys? Do they point to anything specific? Thanks.

Matt

 

I did use an infrared thermometer so the readings should be accurate. I checked each several times. They bounced around a little, but the numbers above are pretty darn close. I still don't understand that increase in temp after the second O2 sensor.

Matt

 

This is really strange, and all the usual disclaimers apply... After resetting the PO420 regularly every 200 to 2,000 miles and basically giving up, It's now been over 5,000 miles.

I ran out of gas about 10 miles from a gas station, and all I had was about a gallon of 2-stroke premix. Crossing my fingers and hoping I didn't do something bad to the system, I put the premix in, made it to the gas station and filled up. A week or so later I reset the code.

That was months ago, and it hasn't been back.

I have no idea if or why that worked - all I know is no more PO420...

 

i reset my p0420 many times over the past year, every time it would come back in about a week.

about a month and a half ago, it shut off on its own, and stayed off. I figured for sure the supercharger would kick it on again, but the charger has been on for a month and no light.

I think the worst part about this light, is that there is no running issues, and even a replacement aftermarket cat will still kick the light. only the $2000+ toyota factory cats turn the light off, and even then im not sure that will solve the problem in the long run.

if my light comes back, Im going to replace the o2 sensors. if that doesnt do it, im ditching the front cat, replacing the rear with a decent aftermarket one, and using the urd o2 sim. bye bye light.

 

Does your handheld show data? You'll need to see how fast the o2 sensors are switching, you may have a lazy o2. The P0420 code sets if the ECM sees the precat o2 isn't switching about 4-5 times as fast as the post cat o2. You might need someone with an experienced eye take a look at the data though, it can be hard to tell the diff between a bad cat and a bad o2 for a non-tech. If you end up replacing them make sure you use OEM o2's, trust me on this. And like someone said above, check with your dealer to see if the emissions system is still under warranty, many are 75k+.