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2001 GS300 P0420 and P0430

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Old 06-01-15, 09:32 AM
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20012003rx
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Default 2001 GS300 P0420 and P0430

Hi all,

I recently got the codes P0420 and P0430. I have read several threads about this, however I have not read anything that was truly helpful...

Symptoms include:
1.) A rough idle; my entire car vibrates.

2.) There is a broken clamp hanging from the exhaust (located at about the middle of the car, between the back seats and center console).


Possible reasons/solutions:
1.) Could it be that the broken clamp was holding together a seal and I need to replace the clamp so the seal is fixed? (i.e. there is an exhaust leak?)

2.) Should I ground one of the spark plugs, hold the throttle at 2500 rpms for 2 minutes, and try to clear the cat of any contaminants?

3.) Or should I replace O2 sensors? If so, which ones? Are they downstream or upstream? And where are they located?

Thanks everyone!
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Old 06-01-15, 10:36 AM
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DMPesso
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start with the exhaust as most 420/430 codes come from air leaks which could be from the broken clamp. First, ENSURE there are no leaks before proceeding to the next step as that is the most common cause and cheapest fix. If its not a leak I would check O2 sensors on the bank that your CEL is for. I have never heard of spark plugs causing 420/430 codes. O2 sensors or exhaust leaks can make your entire car vibrate at idle, but so can motor mounts.
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Old 06-07-15, 08:02 PM
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I just had the P0430 code on my 04 GS300. It turned out to be a leaking exhaust gasket that was between the exhaust manifold and the mid pipe. I would check that out.
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Old 06-09-15, 07:19 AM
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20012003rx
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Thanks guys, I will check it out as soon as I can and let you all know. It might be a couple days though. I will check the exhaust gasket that was between the exhaust manifold and the mid pipe, and go from there. I was also told to pour a small amount of Seafoam in the intake and see if there is any blue-ish smoke that comes out from the exhaust to check for leaks. So I might try that. I do have a broken clip underneath the car located at the mid pipe and exhaust manifold, so I will start there.

Thanks again, and I'll keep you all posted!
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Old 06-10-15, 06:27 AM
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Please check your air hose in your intake manifold as well That also made thoses code in you car. But definelly check the leak too. I have pictures for the hose that youcan check as well. Good luck and I hope you fix that leak onyour car soon. Tell us what are you found please.
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Old 06-13-15, 10:05 AM
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MCON, thanks for your response! I checked all intake and exhaust gaskets. There are not leaks in them So, I had it checked out by two friends who used to work as mechanics and in emissions, and they both said it's both of my cats. Fairly easy fix... I found two of them with seals for like $450.

I can replace them, but is it worth it? The car has a tie rod issue too, and has 227K miles on it. Thinking of scrapping the car for a newer one...
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Old 06-13-15, 10:22 AM
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Originally Posted by 20012003rx View Post
MCON, thanks for your response! I checked all intake and exhaust gaskets. There are not leaks in them So, I had it checked out by two friends who used to work as mechanics and in emissions, and they both said it's both of my cats. Fairly easy fix... I found two of them with seals for like $450.

I can replace them, but is it worth it? The car has a tie rod issue too, and has 227K miles on it. Thinking of scrapping the car for a newer one...
If you were not so far from me, I offered $$$ for it and I personally driving back that baby to my house.
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