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P0420 CEL

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Old Dec 27, 2007 | 09:08 PM
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Default P0420 CEL

this is the second time the car has thrown the code. the first time was over a month ago (easily over 1000 miles driven). when it threw the code the first time, i thought i was just a fluke, so i cleared it and went on my way. but now that its back, what could it be? and why did it take so long to com back on?

i thought it would be tha cat, b/c i read that the s/c kit likes to spew oil into the cat and clog it up, but my motor hasnt been eating any oil (knock on wood) and it took over 1000 miles to throw the code again. could it be a faulty o2 sensor?

what could be the problem??

Thanks for the help

Dan
Old Dec 27, 2007 | 09:50 PM
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SC spewing oil into the CAT?? The SC does not sit in the exhaust manifold, so I dont see how in the world that would happen.

That code should either be a bad cat or bad secondary O2 sensor.

Do you have the proper tune in place for the SC ?
Old Dec 28, 2007 | 12:19 AM
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the spewing oil thing is just what i read...i assumed that it ment that oil made its way through the exhaust manifold to clog the cat....but like i sed i havent had any loss of oil...so i dont think that that is the problem.

yes about the tune... its the TRD tune right from the dealer, i had the dealer do the install.

should i just take it to the dealer and see what they say?? is there somthing that i can do to test and see whether its the cat or the o2 sensor?
Old Dec 28, 2007 | 04:22 PM
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Cat died, mine did 3x, 2x after supercharging
Old Dec 28, 2007 | 04:28 PM
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If you don't have an aftermarket header or s-pipe, and you got it done by the dealer, take it to them. It should be covered.
Old Dec 28, 2007 | 04:34 PM
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yeah its warantied for 80k
Old Dec 28, 2007 | 07:03 PM
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Yuo is the cat.....I just did it....
Old Dec 28, 2007 | 10:25 PM
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It doesnt hurt your car if it doesnt get fixed, its just your gas mileage goes to ____ and you run superduper rich
Old Dec 28, 2007 | 11:48 PM
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And you can't pass smog check.
Old Dec 30, 2007 | 04:51 PM
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ok, thanks guys...ill just take it into the dealer and see what the say.

Thanks again

dan
Old Dec 31, 2007 | 07:13 PM
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explains my crappy gas mileage.... Is this the cat on the header? I think I'm just going to get a header.
Old Jan 2, 2008 | 05:29 AM
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No its the second one, after the front sway bar.
Old Jan 2, 2008 | 10:40 PM
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so the cat that is on the midpipe is the one that is bad?? i would have thought that it was the pre-cat. so i can fix this by getting a new mid-pipe?
Old Jan 2, 2008 | 10:46 PM
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you dont' need a new midpipe. the anti fouler trick will work for you. What did the dealership say?
Old Jan 2, 2008 | 10:56 PM
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i finally got an appointment for this Saturday, so im gonna see what they say.
Old Jan 3, 2008 | 12:16 AM
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The two O2 sensors measure the precat (the one on the header) which is why getting a header with no cat on it causes the CEL and requires the antifouler or relocating the second O2 behind the other CAT.
Old Jan 3, 2008 | 08:23 PM
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So if you are getting this check engine light, does that mean that your cat is bad? I've been getting it ever since I put the SC on. I have my scangauge hooked up so I would just clear the code when it turned on. Now it comes on so frequently that I stopped bothering to clear the code.

I guess my question is, if I do the antifouler trick, is that a sufficient fix or is the cat damaged to the point where it would cause performance issues and need to be replaced?
And does it really make your gas mileage suck? I've been getting 21 to 23mpg and I don't whomp on it that much at all.

Thanks!
Old Jan 3, 2008 | 08:34 PM
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And wait... Don't tell me that this Anti-fouler is really only a 3 dollar part from auto zone. I'm going to kick myself for not doing it a long time ago.

quote"*Note* The DC Header is known to make the 'check engine' light pop on, But no worries for $3.00 at your local Autozone Or Pep Boys you can fix this.

You will need a set of Spark Plug Anti-Foul's they are 18mm HELP! brand Part#42002 or 42009. "

Does this sounds about right? I quoted from this thread about headers, but I assume it is the same.

https://www.scionlife.com/forums/viewtopic.php?t=56520
Old Jan 3, 2008 | 08:43 PM
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Yes. you are correct sir. but like I said before, the SC alone should not cause this, and if you do not have an aftermarket header, you should have your dealer look at it under warantee. If you wait and put the antifouler in there, it will mess up their readings. Oh, and the anti fouler does not work 100% of the time anyway.
Old Jan 3, 2008 | 09:44 PM
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I've got the factory header right now, and what looks like a blown head gasket. And no warranty. So I got lots of work to do. I figured since I'm going to have the head off, I might as well install an aftermarket header, and the anti fouler. That should hopefully do the trick.



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