artfil91

Welp, I think it's time for me to come to terms with the fact that my bank 2 (driver's side) cat failed on my 2009 GS350 AWD. Fixed exhaust leaks, tried CataClean, switched fuel brands, and that stupid P0430 keeps coming back.

With that said, are the rockauto replacements suitable? With shipping I can snag one for under $500.... dealership has them for literally triple that amount so that's out of the question.

https://www.rockauto.com/en/catalog/...converter,5808

An independent exhaust shop locally warned me about buying a non OEM cat; supposedly these cars may still trigger the error code unless it's OEM. Is that true? Has anyone else experienced this?

Thank you

artfil91

I also found this option on eBay... a new catalytic converter for under $200 seems too good to be true but I was curious to see if anybody has had any luck with them:

https://www.ebay.com/itm/33433101972...gAAOSw5cRZKEUQ

LeX2K

Eastern is okay assuming it fits properly which it might not. I have not personally been snagged by a CEL with aftermarket catalytic only read about it. Avoid that Ebay seller a 92.8% rating is atrocious about the lowest you will see.

93SCMax

Have you confirmed it's not your downstream O2 sensor? Replacing it is so much cheaper and easier than replacing a catalytic converter.

artfil91

Yes, I replaced it, code came back 30 miles later

Lwerewolf

This gen of GS has wideband O2s (AFR) at the front and measures cat efficiency in a different way - it estimates oxygen storage capacity. There are some patents by Toyota that probably explains in close approximation how their system works, but the gist of it is - it's not just switching between lean/rich all the time and expecting a relatively flat line on the post-cat sensors.

I'd go for as-low-as-possible mileage used. Of course, check for leaks near the cat (including after the secondary O2s). The secondary O2s generally become lazy over time, they shouldn't be the reason for a p0420/0430 - people mod low pass filters to fool the ECU.

LeX2K

Do you mean used catalytic converter? At least around here only way you'll find that is on the black market.

Lwerewolf

Breakers can't sell the whole manifold or something? I wouldn't bother getting just a converter, unless it's like the, say, 1/2/3LS design where it bolts on right after the log manifold (IMO the best design from a serviceability PoV).

artfil91

No leaks, I actually found a tiny one in the flange by the end of the shop, had it fixed but the code still came back. Replaced the downstream O2 sensor as well; no luck. When you say "low pass filters" are you referring to o2 sensor spacers?

Finding used cats is next to impossible, not to mention that they usually come from sketchy sources. Would had to go through the trouble of a swap only to find the replacement is bad, especially seeing that this appears to be a common failure on these cars.

Lwerewolf

https://en.wikipedia.org/wiki/Low-pass_filter

Used exhaust manifolds off of eBay or something...?

artfil91

There's 1 available at the moment... but it's the bank 1 side for a RWD car. I need bank 2 for AWD.

ibidu1

iTrader: (1)

Did you remove all of the tin covering on the mid pipes? The awd mid pipes have a design flaw in that the tin covering, the inside fiberglass matting holds moisture slowly rots out the pipes. I would completely remove the tin covering, put the car on jack stands. With the car running have someone block off both tail pipes with rags. This will help force air to make sure theres no leaks.

Also you can take measurements with a lazer thermometer, measure the inlet and outlet of the cat and verify it is the same on both sides. If one cat shows a lot less heat exiting then its probably blogged. That being said cats do not just go bad on our cars, unless you have a bad misfire and unburnt fuel was able to pass through.

I would try to avoid aftermarket cats, they do not last aslong as oem. I would wait for a used one, maybe look on facebook for someone parting out a lexus gs awd. Even if it was a rwd, maybe you can cut those cats and have a muffler shop weld them in

artfil91

I've read about that tin covering on the AWD midpipes... my car doesn't have that. I think they tweaked the design of the exhaust for the 2009+ MY cars. I've inspected the exhaust several times myself and had 2 shops look as well, a tiny leak was found in the flange about 8 inches in front of the downstream o2 sensor, but it has been since fixed and the code still returned.

I can check the temp like you mentioned but vehicle performance is just fine with no bogging or anything suggesting a clogged cat.

However I would have to disagree with you in terms of failure rate.... cat failures seems to be a common issue on these cars, a search on this forum and other Lexus groups will reveal a lot of P0420/P0430 issues. I've owned this car since December 2020 and never had any issues with misfiring; perhaps the previous owner neglected it at one point but not while it was in my ownership. It is worth pointing out that my car consumes some oil as well (about 1 quart every 3k miles) so that may have fouled them.

93SCMax

I believe everyone is offering advice to help you resolve your issue, without going the most expensive route. P0420/P0430 codes are common, but my experience is that the cat is the most expensive fix and only one of many things to throw the code. I've had P0420 and P0430 codes. My fix was replacing the rear O2 sensor, a spark plug change, and injector cleaner with known premium gas. You've done due diligence replacing the rear O2 sensor and chasing down at least 1 exhaust leak. I think it's prudent to also check/replace the upstream O2 sensor and absolutely block off the tailpipes to confirm absolutely no leaks. If you've convinced yourself all else is fine, then replacing the cat is the thing to do.

When the rear O2 sensor was replaced, did you use a genuine Lexus O2 sensor or a genuine Denso equivalent?

Also, if you are burning 1 qt of oil every 3k miles, you may have carbon build up on rings/valves in that bank. It's possible the front O2 sensor has seen more unburnt fuel/oil than designed so the ECM check between front and rear O2 readings is throwing the code.

If it runs well, great, but have you considered pulling the plugs from cylinder's 2,4 & 6 and reviewing?

Good luck.

artfil91

I absolutely appreciate that, I REALLY don't want to replace the cat but I feel like I'm running out of options. I haven't pulled the spark plugs recently however they are relatively new, I replace all 6 about 15k miles ago with OEM Denso units. I can check them again though. The old ones showed minor evidence of oil consumption but nothing concerning from what I remember. I also believe they were original to the car (about 115k miles on them if I remember correctly). I changed them at least 8 or so months before the car started showing the P0430 code.

I also changed the PCV valve (bought from Lexus dealer) about 7-8 months ago in the hopes it would reduce oil consumption but doesn't seem to have made much of a difference.

Let me summarize exactly what I've done to the car so far to address this issue (all of this took place within the last 2 months) -

• Inspected for exhaust leaks and resealed both exhaust flanges (where the manifolds meet the mid pipe), only spots where leak was found
• New fuel cap (long shot I know, but the CEL at one point briefly shut off after a fuel fill up so I wanted to rule it out to be safe)
• Replaced downstream bank 2 O2 sensor with OEM Denso unit
• 2 bottles of Cataclean in the fuel tank at 1/2 full, ran for about 150 miles and refilled with 93 octane Shell v-power gas (normally I use Kirkland fuel from Costco due to price but I wanted to ensure the issue wasn't fuel quality related)
  • May be worth pointing out that the CEL took a bit longer to return with Cataclean in the fuel tank (normally comes back after 20-30 miles after clearing, with cataclean it was closer to 100)
• Fresh air filter (Denso) and oil change (mobil 1 5w-30 high mileage with OEM Toyota filter). Can't imagine these two things having any effect on the cat code but again, just wanted to list what I've recently done to the car.

Like I said, the car feels fine, drives great, and has no other problems other than the P0430 code and minor oil consumption but that seems to be a characteristic of many high mileage 2GR engines. I say minor because 1 quart per 3,000 miles doesn't SEEM terrible; I've seen other 2GR owners going through that amount in less than 1,000 miles. When revving the engine in park, there is SOME blue/black smoke that comes out of the exhaust but only at high RPM.

I'll inspect the bank 2 spark plugs again soon along with the upstream O2 sensor; you think that an issue with the UPSTREAM sensor can ultimately cause the P0430 code? Never had a code related to that O2 sensor yet.