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Code p0420 & p0430

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Old 07-28-14, 07:59 AM   #1
STREETGS
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Default Code p0420 & p0430

So my check eng light came on,
and it gave me these two codes
(p0420 bank 1 catalyst efficiency below threshold)
(p0430 bank 2 catalyst efficiency below threshold)

some people told me its my o2 sensors, others that i need a new catalytic converter.
Have not taken in to a shop yet, what do u guys suggest i do to rule out either catalyst or 02sensor ???

Has anyone had the same codes?

(2001 gs 300)
160k
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Old 07-28-14, 08:03 AM   #2
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I've had the same P420 code on my GS400. The car wasn't running for a few months, then I swapped in a new 1UZ-FE. I got the error about a month driving it in. it's either the o2 sensors or the cat. I would definitely check the o2 sensors first since they are the cheaper fix. After replacing the o2 sensors and you still get the code, it's probably your cat
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Old 07-28-14, 10:47 AM   #3
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Hook your car up to a decent scanner that shows the O2 sensors' activity. There are a couple things that may trigger the codes. I had the same ones on my car and it turned out to be a leak where the cat and the exhaust manifold bolts up. I wouldn't start replacing things randomly.
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Old 07-28-14, 11:45 AM   #4
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it is MOST DEFINITELY your O2 sensors or an exhaust leak, 99.9% of the time its NOT the cats as these cats are built to last forever, it only says CAT because something is causing the CAT to run below its threshold, IE: the sensors or a leak preventing proper air flow. Don't ever listen to anyone if they say its the CAT, I know a few people that got taken for a nice ride by their mechanic because they saw the word CAT and they listened to him and changed the cat, spending over $1,000 and all they had to do was change the O2 sensors. This isnt a cheap american car with cheap cats that can be replaced for $500. These cats are built to last a lifetime, only way they go bad is if they are damaged internally by cracking from an accident or something.
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Old 07-28-14, 02:13 PM   #5
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These guys are correct, I had a leak at the gasket on the cat that caused this code. Get under there and check for leaks, next would be the o2 sensors if there aren't any.
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Old 07-28-14, 02:37 PM   #6
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lets hope he didnt already change his CATS, lol...
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Old 07-29-14, 06:53 AM   #7
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Thanks guys, oh no i have not replaced anything yet
i decided to consult club lex first to get guided in the right direction as to what to do,

what readings should i see when viewing the 02 sensors on the scan tool?

I will be inspecting it over the weekend


thanx.
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Old 07-29-14, 08:03 AM   #8
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I wouldn't even bother wasting time testing them. I would simply FIRST check for an exhaust leak which is easy have someone press the gas while you feel around or listen for any air leaks. Then if you are positive there is no leak then change the o2 sensors all at once so you never have to bother with them again. Or if your not trying to spend that much just replace the sensors in the banks the CEL came on for. Guaranteed to be one or the other.
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Old 07-29-14, 10:10 AM   #9
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How many 02 sensors does this car have? 6?
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Old 07-29-14, 10:41 AM   #10
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2 on the GS 300, 4 sensors on the V8's
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Old 07-29-14, 11:40 AM   #11
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Quote:
Originally Posted by GSteg View Post
Hook your car up to a decent scanner that shows the O2 sensors' activity. There are a couple things that may trigger the codes. I had the same ones on my car and it turned out to be a leak where the cat and the exhaust manifold bolts up. I wouldn't start replacing things randomly.
^^This is the correct course of action.
I wound not start replacing good parts at random, mainly because I have more time than money for these sorts of things...

I use a Ultra Gauge in the car and one of many features is reading activity from O2 sensors in real time.
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Old 01-13-15, 01:51 PM   #12
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Quote:
Originally Posted by STREETGS View Post
So my check eng light came on,
and it gave me these two codes
(p0420 bank 1 catalyst efficiency below threshold)
(p0430 bank 2 catalyst efficiency below threshold)

some people told me its my o2 sensors, others that i need a new catalytic converter.
Have not taken in to a shop yet, what do u guys suggest i do to rule out either catalyst or 02sensor ???

Has anyone had the same codes?

(2001 gs 300)
160k
Replacing manifold gaskets solved the same problem in my 2001 GS430. My usual service center, the local Toyota dealer, had insisted that the both catalytic converters needed to be replaced and quoted me about $3K (about 90,000 miles at the time). I didn't believe this was likely so I sought a second opinion and had the problem solved at 1/10 the cost.
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Old 01-13-15, 02:45 PM   #13
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The GS300 has 4 O2 sensors, not 2 like posted earlier
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Old 01-13-15, 04:17 PM   #14
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Quote:
Originally Posted by Spencerfg View Post
Replacing manifold gaskets solved the same problem in my 2001 GS430. My usual service center, the local Toyota dealer, had insisted that the both catalytic converters needed to be replaced and quoted me about $3K (about 90,000 miles at the time). I didn't believe this was likely so I sought a second opinion and had the problem solved at 1/10 the cost.
Out of curiosity what did they charge you to replace the manifold gaskets because my 2001 GS430 was making an annoying rattling farting sound because air was leaking out the manifold. It was a very labor intensive job. First place quoted me 1000 to remove the engine and change them. Then I went to somebody else who charged 700 and I still feel like i overpaid
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Old 01-22-15, 09:49 PM   #15
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Quote:
Originally Posted by DMPesso View Post
Out of curiosity what did they charge you to replace the manifold gaskets because my 2001 GS430 was making an annoying rattling farting sound because air was leaking out the manifold. It was a very labor intensive job. First place quoted me 1000 to remove the engine and change them. Then I went to somebody else who charged 700 and I still feel like i overpaid
This was about a year and a half ago. The total bill was around $300.00 including a second state emissions inspection ($28.00). This was from an independent mechanic in northern Virginia who specializes in Lexus. I found him through YELP and went to him because of the incredibly and consistently good reviews. After this experience I added my own favorable review and will go back to him if another problem arises, even though it's a 60 mile drive.
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Old 01-22-15, 09:49 PM
 
 
 
 
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