As I recently posted, I had this happen and am suspicious that it might have been caused by poor fuel. Try changing your fuel source and see if the problem corrects itself.

 

Also ran into this problem and disconnecting the battery fixed the issue...

 

Agree, fuel does affect it and the fuel grade too. I never had problems with regular field at costco, but now I do.

And I am not sure but I think a long drive also helps. Like 100 miles trip.

U need to do more homework. It doesn't fix the problem, the code just cleared and take awhile to come back. You won't pass the emission test with your disconnect battery fix because it will showed that power was lost and not all fault codes are registered. They will tell you to come back after driven around 70 or 80 miles.

 

Here's an update. The light stayed out for a few weeks, then came back on for a week. Then it went out again (long enough to pass emissions inspection) but it's currently on. I've been cautious about fuel so I no longer think that was the root cause of the problem. BTW the same thing happened to my RX and it started the same week. That's why I first suspected fuel. If I were up to it, I'd inspect and clean the O2 sensors but I'm too lazy for that.

So I'm still looking for suggestions.

 

How many tank a week do u go through? It seem 1 tank a week will keep this code away.

 

check your exhaust for leaks... i had the exact same issue and i thought it was bad gas too... but when i got the car up in the air and sprayed soapy water on the flange just after the driver side crack, it was leaking... i ordered all the gaskets and replacement nuts and bolts... hopefully i can get to it tonight... i am also due for emissions inspection this month so have to get it fixed...

https://www.clublexus.com/forums/gs-...and-p0420.html

admins/mods, can we possibly merge these two threads?

 

That exact thing happened to me about three years ago so I can confirm your fix works. The dealer was insistent that both catalytic converts had to be replaced. I didn't buy that so took it to an independent mechanic who replaced the gaskets. That fix lasted years but now I have the problem on one side. I no longer trust the dealer.

 

Dealer go by the book. The book say when the CAT say something is wrong, replace A,B,and C.

But that's not the real problem. It sux our exhaust pipe is so easily rust through. I don't see that in the Honda much older. I think lexus went cheap on the exhaust pipe.

 

so i managed to get thru the rusted bolts and swap the gaskets out... unfortunately after all these years, the salt and rust ate through the bottom half of the flange... i can see the bottom of the gasket after everything is bolted up... i tested for leaks and it looks like the washers are holding everything closed, but i hear a leak now in the y-pipe underneath the heat shields... CELs are still on from the leak... i have the feeling it's leaking at where the heat shield touches the pipe or at the y... i'm going to try and see if i can cut off the heat shields and find the leak... patch them for inspection to buy me some time until i can find a replacement...

does anyone have a pic of how/where i cut/unbolt the heat shield on a 430 y-pipe?

 

a note to everyone. remove your damn heat shields!!! those things do nothing but trap salt and crap and rust out the pipes... removed the front shields on the y-pipe found a hole on each side about the size of a dime... welded them shut but then heard more leaks down the pipe... removed the rear shields closer to the 3rd cat and found more holes... replacing the y-pipe now... $700 later...

 

Everyone. I got code P0430 couple days ago. Thanks to google and CL. I "reset" the ECU (remove the "-" from the batter for 10 min). The engine light is gone. I drove for 25 miles today and it has not come back yet.

 

you will notice that over the next few months the CEL might come and go occasionally... that is usually how it starts...

check your flange for leaks... i sprayed soapy water on it and it started to bubble... if you can get the bolts free and change the gaskets yourself, it's a $30 fix...

 

Hi guys, new guy here. Just had to jump in and stand up for my brothers. MECHANICS ARE NOT BAD!! We are awesome. Not all of us are monkeys with wrenches, throwing parts at cars randomly hoping to fix something. We're not all criminals. The problems is, just like any profession, there sure are some bad one's out there.

The problem lies in your expectation's. You expect good and cheap. You only get one, you pick. The good ones are at dealerships and a select few hardcore independents.

As far as the OP's codes, general catalyst efficiency failure

1. Check exhaust system for leaks, especially in front of the cat or near the Air/fuel sensors. Leaks after the downstream A/F will not effect the catalyst monitoring system. Be sure to check your exhaust with the system DEAD COLD (8 hours engine off). No leaks??

2. With engine at operating temperature, observe A/F sensor data. Be sure all sensors are switching from high to low (rich to lean) in a somewhat consistent pattern at a steady RPM. You can all but assume they are if the only code your getting is a 420/430. Otherwise, the ECM would also flag for A/F inactive or implausible signal or a circuit fault.

3. If you have NO exhaust leaks, and all of your A/F sensors are working correctly, then your converter is bad. It is no longer doing what uncle sam wants it to and is condemned to be recycled. The guy that recycles those things lives in a really nice house. Seems legit.....

I've heard recently that they now have a 'catalyst cleaner' available over the counter but I've heard of no-one using it with any amount of success. I've have limited success washing them out with GM top engine cleaner and sea foam and a few drops of dexron3 (automatic transmission fluid). I would never personally or professionally do that to my own vehicle. Replace the converter. Don't be mean to the Lexus. It deserves better.

I'd want to see what your fuel trims are at op temp and a steady highway speed, throttle snaps, etc before I went any further. Make sure your engine isn't running too rich or lean. This is the #1 cause of catalyst failure. Don't fix the symptom and miss the cause.

 

My 04 rx330 has both codes as well. I've removed both cats & soaked them in dish detergent overnight. The catalyst is intact, unburnt & clear. New exhaust gaskets & vacuum lines. My MAF seems to be operating properly. The upstream air/fuel sensors are new (Denso). Downstream are the correct Denso splice-ins. Spark plugs & intake gaskets are new as well. Looking at my LTFT it seems to be running a bit lean.

 

The FT readings you posted above are good. I would not be concerned at all about the fuel mixture occurring in that car.