P0420 P0430- troubleshooting. (1 Viewer)

[crujonesisradd]

Hello everyone. I've been fighting the dreaded P0420 P0430 on my newly acquired 07 GX470 with 190k miles.
I've been searching for days-hoping I can find it's not cats since it's running very well; getting great mileage (18.4 avg on last tank with a light foot in CO) with plenty of power. I've always been under the impression that bad cats kill both of these.

Runs perfectly fine, but throws CEL, VSC and TRAC christmas tree lights.

Here's what's been done in the last 5k miles.
OEM Throttle body (clean)
OEM MAF (clean)
OEM up & downstream 02 sensors
OEM gas cap

After the codes thrown, and the parts thrown at it (mostly by previous owner) , what would you guys recommend next?
I live in Denver, so unfortunately we have to be CARB compliant with cats, so catalytic converter replacement is the very last thing I'd like to go after due to price.

Anything I'm missing, other than just replacing manifold/ cats?

 

[masturv8]

That looks like a Hewitt SAIS delete kit. There are multiple types. That and your MAF have nothing to do with your more-than-likely bad catalytic converters which are causing P0420/P0430. You can plug that back in and leave it in place, it's a good thing.

Are your cats factory original or replacements? Or are they missing entirely? The exhaust manifolds on these trucks typically leak, causing a ticking sound. If it goes to long it will fry your cats. If they were replaced with aftermarket, those may not leak but the cats are poor quality and will fail.

P0420 and P0430 only trigger if your downstream catalytic converter is not reading cleaner air than your primary O2 sensors, letting you know your cats are 1. BAD, or 2. MISSING. This is especially likely if those are the only codes you are getting.

If you simply do not have cats, get a Yotawerx (sp?) tune. They can delete the code permanently.

If your cats are actually bad, or you have the exhaust leak (ticking sound) then replace them. You'll do engine damage over time running bad or clogged cats.

https://hewitt-tech.com/product/secondary-air-injection-system-bypass-kit-gen-1-v36h/

 

[Rednexus]

It's fairly unusual for the cats to be die on a well-running engine. The OEM Toyota cats are very high quality and can last hundreds of thousands of miles. However, if the P.O. ran the engine where it had some other kind of issue (such as running overly lean/rich), that may have killed the cats. I'd suggest plugging in a good OBD2 reader and checking fuel trims, air fuel ratios, etc to make sure there isn't some other issue that killed the kits.

If you do indeed need new kits, I highly recommend a set of headers instead. If they are not currently backordered, Doug Thorley short-tube headers will be around the same price as OEM manifolds and will keep you from ever having the dreaded exhaust leak in the future. You'd need to order a new set of aftermarket cats to have the welded in place of the OEM cats. If you don't have a visual or tailpipe emissions inspection (just OBDII reader check), you can also install long-tubes and completely skip the upstream cats (which is what I did - but we have zero emissions here in MO).

 

[HomersCanyonero]

I fought my cats for over a year (replaced all O2 sensors, cleared codes P0420/430), read the odb2 fuel trims, and even considered using a cat cleaner.

I’m in California, so I bit the bullet and got two new Lexus integrated car exhaust manifolds back in Feb 2021 on sale for about $438 each plus tax and free shipping. I also bought new gaskets. My local Indy mechanic installed both for $200 total. Not sure what he was thinking, but honored his labor price.

Ever since then, zero codes and I pass smog with ease! And I feel I did the environment right.

I bought my 2003 gx470 in March 2017 and the P0420/430 codes got worse over time as in more frequent. Used to clear and last like 500 miles before they came back…until they would come back every 50 miles.

I also got P0171 and P0174 but cleaning the MAF and replacing the O2 sensors helped with these codes.

Anyway, my point is that I solved my problem with new integrated cats from Lexus. It’s going to be 3 years now and no issues since then.

 

[white_lx]

If fuel trim numbers and A/F sensor active test shows that everything is working fine, my next step would be an 'oxygen storage test' to check the condition of your catalytic converters. That is probably the best (only?) method to determine the health of your catalytic converters and be 100% sure that you need new cats.

This video is a good example of how to perform the test and what it should look like for a depleted cat vs a newer cat. You are looking at the time difference between the A/F going rich/lean and the secondary O2 going rich/lean. That time difference is caused by oxygen released/absorbed in the catalytic converter. A good cat will have several seconds delay.

 

[StrongIslandGX]

I got the same P0420 code and I installed O2 spacers and have not had a CEL since (knock on wood). Check out this thread:

P0420 wont leave me alone..

I recently purchased an 05 GX470 and after putting about 600 miles on it or so, the code popped! Well just for s***s and gigs I ran some 44k through it and cleared the code hoping it might help clear it out... Long story short the code is coming on more and more often about every 50k miles if I...

forum.ih8mud.com

 

[masturv8]

I got the same P0420 code and I installed O2 spacers and have not had a CEL since (knock on wood). Check out this thread:

P0420 wont leave me alone..

I recently purchased an 05 GX470 and after putting about 600 miles on it or so, the code popped! Well just for s***s and gigs I ran some 44k through it and cleared the code hoping it might help clear it out... Long story short the code is coming on more and more often about every 50k miles if I...

forum.ih8mud.com

Short term fix. Doesn’t change the fact that you prob need new cats.

 

[Rednexus]

Short term fix. Doesn’t change the fact that you prob need new cats.

Depends on where you are located and the level of emissions testing. If a cat is not plugged but not functioning well at it's job as a cat, the engine can be run indefinitely with a downstream O2 spacer with no ill effects. I did this on my last beater (a Subaru) over a decade ago and my neighbor is still driving it. The cat is not plugged, it's just not burning off stuff very well. My current GX has the upstream cats deleted for long tube headers, I also have the 90 degree spacers and have had exactly zero P0420/430 codes over the past 2.5 years. The spacers really work that well.

But....if you have a visual inspection or tailpipe sniffer smog test, the presence of the spacers will be immediately noticed, and new cats would be required to pass.

 

[masturv8]

Depends how it fails. If it gets plugged or partially plugged you can 100% toast your valves from heat buildup. Ask how I know

They can also catch spark plugs that break off inside the combustion chamber and get plugged that way, happened on my Dad’s 480k mile 4runner.

 

[bgilly]

If your local regulations will let you get away with spacers, they’re worth a shot. Inexpensive to acquire and install. Worked for me.

 

[crujonesisradd]

To be very clear (as noted in the original message), I AM in Denver, and we have full visuals and emissions testing.

The o2 spacers are workaround, and don't actually fix anything other than turning off the light.

About to pull the trigger on new manifolds/ cats.

 

[Rednexus]

If you can swing it, I would definitely recommend Doug Thorley short tube headers and replacement (non-OEM cats). This will get around the OEM-style manifolds cracking again in 5-6 years AND give you more power. The OEM manifolds are a really bad design in a lot of ways, the headers fix most of the design flaws. You'd still have cats and would not need any spacers or other trickery with this setup.

FYI you can probably sell your old cats as well. I got $585 out of mine a couple of years ago.

 

[crujonesisradd]

If you can swing it, I would definitely recommend Doug Thorley short tube headers and replacement (non-OEM cats). This will get around the OEM-style manifolds cracking again in 5-6 years AND give you more power. The OEM manifolds are a really bad design in a lot of ways, the headers fix most of the design flaws. You'd still have cats and would not need any spacers or other trickery with this setup.

FYI you can probably sell your old cats as well. I got $585 out of mine a couple of years ago.

I'm in Denver, we can't use non CARB cats, they run visuals and emissions.

 

[Rednexus]

I'm in Denver, we can't use non CARB cats, they run visuals and emissions.

You can buy non-OEM CARB-compliant replacement cats and install them with the short-tube headers.

 

[moridin2002]

You can buy non-OEM CARB-compliant replacement cats and install them with the short-tube headers.

Non-OEM, non-OBD-II cats tend to go bad a lot sooner. The 05-09 GX Doug Thorley headers have a CARB EO pending. The 03-04s have been certified. Magnaflow is now selling CARB OBD-II compliant cats, but you would have to contact them to figure out if you could get new compliant cats for the GX that are divorced from the manifolds so that you can weld them to a (hopefully, in the near future) CARB compliant Doug Thorley shorty headers for the 05-09s.

Also, the 05 and newer vehicles have ways of checking for the spacers with on vehicle enrichment and enleanment strategies that happen in real time while driving.

 

[crujonesisradd]

Non-OEM, non-OBD-II cats tend to go bad a lot sooner. The 05-09 GX Doug Thorley headers have a CARB EO pending. The 03-04s have been certified. Magnaflow is now selling CARB OBD-II compliant cats, but you would have to contact them to figure out if you could get new compliant cats for the GX that are divorced from the manifolds so that you can weld them to a (hopefully, in the near future) CARB compliant Doug Thorley shorty headers for the 05-09s.

Also, the 05 and newer vehicles have ways of checking for the spacers with on vehicle enrichment and enleanment strategies that happen in real time while driving.

I agree. The factory manifolds last well over 20 years for the most part. Magnaflow has an option for 2500 / side. It looks like OEM Lexus manifolds / cats are only around 500/ from the dealer online. This will likely be the direction I go shortly to get it done. I will likely never have to mess with them again.

 

[Rednexus]

Also, the 05 and newer vehicles have ways of checking for the spacers with on vehicle enrichment and enleanment strategies that happen in real time while driving.

I have LT's with deleted upstream cats and O2 spacers. Zero CEL's on my 2007 after 2.5 years of running this setup.

The cats aren't the problem I have with the OEM manifolds, it's the manifold cracking and corresponding ticking/exhaust leaks. Toyota never revised the design as far as I know to correct the flaw. Additionally, from having installed them myself the power gains are very substantial with headers. By all means feel free to put OEM manifolds back on - but they will crack again and they will leave the power/MPG gains of headers on the table.

 

[Drunken Ira Hayes]

I brought my F150 and they didn’t do a visual. They don’t know every vehicle, they’re all 17 making minimum wage! As long as it doesn’t throw a readiness code or CEL, you’re good! Plus, they told me (Denver DMV) they can’t prove when it was put on or make you buy new one unless it fails. Don’t overthink it, my F150 is tuned w/aftermarket turbos and catted (Non CARB) downpipes. Evans and Monaco didn’t care, they said,”sweet truck!