I have had the P0430 code for almost a year now and at times the CEL has turned off for a few days. I got a smog check last November after I reset the CEL and I passed fine I guess. About a month ago I scanned the car and I have both P0430 and P0420 now. Yesterday the CEL went off again. I was planning on taking my gs300 to a shop to check for exhaust leaks to try and diagnose, but if the CEL goes off on its own then what do you think is my problem? I read on here that their might be a crack in a hose at the back of the engine but I did not see one when I inspected it.

 

you answered your own question, this one has been asked a million times. Inspect the ENTIRE exhaust for leaks as this is the most probable cause. If there are no leaks then consider your O2 sensors.

 

Get all o2 sensors and exhaust gaskets BEFORE and AFTER cat converters. Get that installed down there nice and tight and your CEL should turn off permanently. I went thru this. I paid for new cats from Sewell. But I could've taken the cheaper o2 sensor and gasket route and had the same result. I poem on having this GS430 for the long run so I had I bought new cats for that reason. Take my advice. Shouldn't be too much. Good luck brother! Let us know what happens! #GODBLESS

 

I think I remember you saying you bought new cats and I was telling you to return them because you dont need them and you were like na Ill change them anyway since I am keeping this car for the long run. I guess it doesn't hurt but thats one expensive uneccesary repair lol.

 

do you notice that your CEL seems to come on after a short restart period? (i.e. you drive a bit then stop and turn off the car for 5 mins, like if you stop for gas or move the car in the driveway... then once you start the car again the CEL comes on?) i seem to have this problem lately...

my P0420 came on 2 months ago. i reset the light and it only came back on a few days ago... i strapped the OBD2 reader to it and checked the live data on my commute to work yesterday and today... there was no codes pending on the initial cold start... but when i shut the cars off for a few mins and restarted it, P0420 went pending...

 

In my case, the intake air hose was in place but loose and crack and I can't see it. The clap cove the crack on the hose.






Also, look the other hose in the other end of this one.

 

thanks... i did see your post in another thread when i searched this common topic... i have the engine cover off so will be able to check the hoses quickly tonight...

 

Are you all saying a loose vacuum line caused your p0430??

 

Yupp I definitely did spend that money on those parts. Haven't seen that check engine light since then either. It was all worth it my bro. Rather eliminate the problem the whole way. No problems since.

 

I've been reading this whole thread. Ima be blunt my friends. 9/10 times the problem with these codes are the GASKETS THAT GO BEFORE THE CAT CONVERTERS AND THE GASKETS AFTER THE CAT CONVERTERS. It's usually air leaks anywhere by the cats that cause those codes to go off. And new o2 sensors. That fixes the problem most the time my friends believe me!

 

the only issue is how do you get the exhaust off cleanly when its been seized on there with all the rust and heat/cool expansions.

 

Cover it in pb blaster. Let it sit for half an hour. Make sure the correct size socket is on securely. Crank off with a breaker bar. All bolts come right off.
Having trouble? Get a longer bar, or use a pipe from home depot/lowes/etc.

 

Unless you meant the pipes/cats seized at where they mate up. In that case, just a brief sharp tug ought to break it loosed once the bolts are off.

 

85% of the time.

 

anyone have the part number for the replacement bolts and gasket? i verified i have a leak on the driver side after cat flange... i sprayed the flange with soapy water and the car started to make bubbles...

also do i remove the nuts or the bolts? im used to seeing a stud and the nut is what secures everything, but when i looked underneath, it seemed like a nut and bolt...