I am still fighting with those 2 codes.I was at one point using custom made spacer just for educational purposes only to see if O2 will be able to give false reading to ecu,but it was working couple days and back to same again, code came up p0420 and p0430.I cant pin point leak if any ,but I can feel smell of gases in the morning when I do cold start.no particular noise but just smell of unburnt fuel still present.
After I use OBD2 code reader to reset this code I am able to drive all day unlimited milage and code will not come back.If you turn off car and turn back on after 10-15 min code will pop up.

I saw only 2 sensors under body after cat,how many are in total?
did any body solve thius problem?
I hope i dont have to buy new cat. to much $$$$$

 

 

thank you for reply RXGS,
you are right There is flange and two like o ring gaskets.
just put some penetrating oil on all 4 bolts,(2 per flange) 13 mm bolt and nut on oposite side was 14 mm.
Using braker bar I was able to remove all bolts and pulled out gasket .It was black on some spots showing sign of leak.
You are 100% right RXGS it was only gasket issue.Here is some of the pictures.

 

Here is how started ,check engine light showed up first.

 

After that code ,it was shoving later on code P0420
,
After resetting code I was able to drive all day ,without check engine light.
D

 

Resetting code with obd2 code reader was just temporary fix,
after you suggestion RXGS I went to dealer and bought 2 exhaust gaskets.
That was solution to my problem.Here you all can see old gaskets how they were leaking.


I have used Cooper silicone for high temperature and did apply allover flange and new gasket.
I hope it will be ok for awhile.
Curing time about 12 hours,just over night.
Next step was to clear code stored in ECU and start driving.
I did noticed bad smell at first due to new gasket and Cooper silicone.
So far so good ,code is not coming back.

Cheers

 

From this diagram it is easy to see location of those gaskets and part number too .


1741OB that was part which was replaced.
if you need more detailed picture ,I hope this next one will help a bit for educational purposes only.



Enjoy your lexus again.

 

Is the Copper Silicone required or just for added measure? I'm waiting to bring my car to my friend who is a mechanic to see if it's my Cat or O2 sensor that's is throwing the code. Who would have guest it was bad exhaust gasket.

 

well silicone was added just in case ,because my flange in the middle was not making perfect seal with gasket.
But there is new update

code P0420 is gone but today got back P0430
and after detailed search under car it was very hard to pin point problem for bank2 (driver side).
I think I will replace whole exhaust manifold on driver side and see what will happened.
now I have to find out wher is good deal to buy one aftermarket or even used.
Reason to go after market is dealership asking over grand for it.
if anybody know any website which is having good price on manifold please let me know.

 

Sounds like your catalytic converters are clogged, take it to a muffler shop and have them test both sides of the exhaust. Also are you getting a lack of power?

If you need new cats you can run aftermarket ones that are much cheaper. Or buy a used set online or at a junkard.

 

^I'd be willing to bet that the CEL is being caused by a leak rather than the cat itself being bad, especially given the fact that the car spent time in Ontario and isn't a 300. I'm not saying cats don't go bad on these cars, but it isn't that common.

 

there is update .exhaust manifold on driver side was replaced.
the new one from dealer was about 1,000.00, I didnt find any after market cat that was in my price range so solution was used one from junk yard.
did find one bout 150 000 miles on it ,without heat shield for about 140 bucks.

my fear was how to transfer shield from the old cat to new cat.Well after operation comenced and when old sucker was out transfering shield was a piece of cake.Also had some fiberglass protection wraped under shield.upstream sensor was replaced with another used one.
installed new gasket from fellpro on the flange and top of intake because I didnt like OEM part from dealer ,too thin and too expensive.
reset code and voila gr8 job all working .

PS
i have used hand wash liquid soap with windex to clean new catalic ,rinse it and let air dry.
so happy now to drive my lexus gs450h
will post some pictures soon regarding this fix
​​​​​​​

 

​​​​​​​Hi, I have a 2007 Lexus GS 450h, European version, and i have P0430 error.
Please, What can i do?

​​​​​​​ Regards,

 

You can check your exhaust for leaks first.