Additives for intermittent P0420 on Toyota 3.0 V6

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So I just got back from a 1700 mile round trip vacation. While I was there, driving around in city traffic, CEL came on. I decided to dump a bottle of Chevron Techron in it, along with the Chevron mid grade for the drive home. 60 miles on IH-10, and code gone! I get back into town on Saturday night, and drive around town yesterday...code back again! Drive to work today on the highway 20 minutes.... code gone again! So apparently, stop and go driving triggers it, and highway cruising resets it. At this point, I'm ready to go full Scotty Kilmer and pour in a gallon of paint thinner on a half tank of gas to see if it helps dissolve any crud in the sensors or inside the CAT. Has anyone tried it?
 
I'd try another round of Techron in it. Sounds like it could use a double or back to back dose.
 
The code comes from a comparison between the front (Upstream) and rear (Downstream) O2 sensors. Additives likely won't fix this...it's more likely the result of old O2 sensors, or an old cat... Both of which wear out with time.

What vehicle? How many miles on it?
 
Originally Posted by Astro14


What vehicle? How many miles on it?


1999 Toyota Avalon. 266K (METHODICALLY & METICULOUSLY maintained by me and previous owner)
 
My GF's 2003 Highlander (with the 2.5L 4cyl that it shared with the Camry) threw this code intermittently. I was informed that it was actually an ECM programming issue related to the sensitivity being set too high for O2 sensor voltage readings. I did a temperature check (front vs rear) on her converter and voltage checks on the O2 sensors. The vehicle literally had no issues. Some people on here used spark plug anti-foulers to pull the O2 sensor part way out of the exhaust stream. In our case I would just clear the code and then it would go for months before throwing it again. A Toyota dealer can probably resolve the issue with an ECN reprogramming, but without knowing more about the issue it's hard to say for sure.
 
If additives don't work (and I'm not optimistic) then I would consider the upstream O2 sensor. It's the one that makes the engine run right anyway, and is often a 100,000 mile maintenance item.

If that doesn't fix it, then I would try the spark plug antifouler on the downstream sensor.

In setting up a new IPD high flow exhaust on a turbo Volvo, I had the same code. I had brand new Bosch O2 sensors, upstream and downstream, so it wasn't the sensors. I added this to the downstream sensor:

https://www.ipdusa.com/products/12093/125604-adjustable-oxygen-sensor-spacer-ipd-125604

Worked great. Code cleared and hasn't been back since. The 90 degree bend keeps good clearance, and allows it to fit in tight spaces.
 
Originally Posted by ripcord
Astro14 is right. It's due for some new O2 sensors with that many miles, but likely is just a worn out cat.


The rear one was replaced last year with a Denso OEM. Front one might be original.
 
Check the bellows hoses on air intake plumbing. They get cracks and cause exactly this strange behavior. On that same engine had cracks on both hose bottoms probably from bending them as they aged to change the air filter. Made the car drive a like new car practically and no sensors were bad. Took me a couple months to look for something different, and there the problem was, got new hoses from Toyota. Any disturbance in air intake after the maf sensor wreaks havoc and sensor codes are thrown. It doesn't mean it's the sensors but the signal they are getting is wrong. Worth a look.
 
Originally Posted by Farnsworth
Check the bellows hoses on air intake plumbing. They get cracks and cause exactly this strange behavior. On that same engine had cracks on both hose bottoms probably from bending them as they aged to change the air filter. Made the car drive a like new car practically and no sensors were bad. Took me a couple months to look for something different, and there the problem was, got new hoses from Toyota. Any disturbance in air intake after the maf sensor wreaks havoc and sensor codes are thrown. It doesn't mean it's the sensors but the signal they are getting is wrong. Worth a look.


You know, I did replace the VCG's last winter.... the big snorkel intake rubber was replaced with brand new two years ago, but the clamps might have slipped. Thanks.
 
Originally Posted by Jarpin
So I just got back from a 1700 mile round trip vacation. While I was there, driving around in city traffic, CEL came on. I decided to dump a bottle of Chevron Techron in it, along with the Chevron mid grade for the drive home. 60 miles on IH-10, and code gone! I get back into town on Saturday night, and drive around town yesterday...code back again! Drive to work today on the highway 20 minutes.... code gone again! So apparently, stop and go driving triggers it, and highway cruising resets it. At this point, I'm ready to go full Scotty Kilmer and pour in a gallon of paint thinner on a half tank of gas to see if it helps dissolve any crud in the sensors or inside the CAT. Has anyone tried it?


Sometimes a back to back dosing of CatClean will help but this may only be a temporary fix if the sensors and Cats are on the decline.
 
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Most of the time, changing the sensors will eliminate the code.
IIRC, there are 2 front and 2 back sensors.
If not, then the catalytic needs to be changed.

This is based on my Brother's Sienna with 3.3L engine.
 
Originally Posted by Jarpin
Originally Posted by Astro14


What vehicle? How many miles on it?


1999 Toyota Avalon. 266K (METHODICALLY & METICULOUSLY maintained by me and previous owner)


That's a lot of use on a cat. Some cars are more prone than others for P420 and IIRC Toyota is one of them, you did good getting it this far. +1 Astro, throw a extension on the rear O2.
 
Ive had luck taking it for a good ride on the highway and locking out overdrive, this keeps the revs up and increases the heat in the cats to try and burn off some of the build up in there. I did this with a double dose of Techron and the light has been gone for over a year in an 04 A4 3.0
 
In March, had P0420 on our RX330 (257,000 miles). Ran back-to-back bottles of Cataclean and Shell Premium fuel for a few tanks. Cleared check engine light manually, passed emissions testing (Colorado) and check engine light has been off for about 5,000 miles. Prior to using, read lots of mixed reviews, but so far, it has worked for our RX.
 
Cat is worn. Mine clogged at 280,000 miles on original and saw non ethanol fuels and PEA additives. Time for a Cat, or go catless and enjoy the HP gains,sound and improved throttle response.
 
Originally Posted by Audios
Ive had luck taking it for a good ride on the highway and locking out overdrive, this keeps the revs up and increases the heat in the cats to try and burn off some of the build up in there. I did this with a double dose of Techron and the light has been gone for over a year in an 04 A4 3.0


Hmmm... this might be worth a try too... cheers!
 
Originally Posted by Marco620
Cat is worn. Mine clogged at 280,000 miles on original and saw non ethanol fuels and PEA additives. Time for a Cat, or go catless and enjoy the HP gains,sound and improved throttle response.


I'm trying to get it past 11/2022, which is 24 years so then I am exempt from emissions testing in Texas and pretty much anywhere in the midwestern states and then the CAT is irrelevant.
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So tried the full gallon lacquer thinner method on half gas tank. Drove exactly 150 miles. No difference in engine smoothness, hums along nicely.

The light had already been off for around 72 hours, but I thought.... could it hurt???
Let's see...

20200701_235258.jpg
 
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Originally Posted by Jarpin
So tried the full gallon lacquer thinner method on half gas tank. Drove exactly 150 miles. No difference in engine smoothness, hums along nicely.

The light had already been off for around 72 hours, but I thought.... could it hurt???
Let's see...


Is this vehicle a 4Runner?
 
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