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Old 05-19-2009, 08:04 AM   #1 (permalink)
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CEL Code P0420, Please Help Me Resolve It

So two weeks ago, my CEL came on while I was driving rather tamely. I took it to an exhaust shop, because I figured the light was probably due to a leak. They pulled the code P0420, "Catalyst System Efficiency Below Threshold (Bank 1)." They said there were no leaks and that the catalyst must have failed and I should replace it. I told them to reset the code and I would see what happened.

Yesterday the light came back on, and I am sure it is the same code (although I will have it checked later today). I have Comptech Headers, an RT Cat, and a Comptech Cat-Back. I'm currently at 35k miles and all of those parts have been on since 3k miles. Is there really a chance that they just suddenly went bad? I have never had a CEL before so I'm not sure why it would start now.

I know I could just get a non-fouler to trick the O2 sensor, but I am worried that there is something actually wrong with the car. The reason for this being that I have been getting worse gas mileage than historically and my engine has been noisy at idle and certain RPMs. Any ideas as to what else might be causing this?

I don't want to just take the car to the shop and say "I think something is wrong" because they will come up with some marvelous reason for me to shell out a grand.

Thanks
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Old 05-19-2009, 08:26 AM   #2 (permalink)
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if the light go's on you will drink more fuel per mile
its normal (safety mode is running much richer)
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Old 05-19-2009, 08:29 AM   #3 (permalink)
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Cheapest, quickest fix (considering you run RT cat), is just to get the defouler.

I run RT cat and defouler. Initially I had the same CEL, but after defouler, it's gone.

At worst case, your O2 sensor is toast, even then, it's not too much to replace.
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Last edited by HoRRo; 05-19-2009 at 08:29 AM.. Reason: o2 added. Reason: o2 added.
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Old 05-19-2009, 08:52 AM   #4 (permalink)
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Okay, makes sense that the car would run richer when it knows the light is on...

What's the story with the correct non-fouler to buy? Do I want the Napa 730-2442 or the Help! 42009/42002?

Still, does it not seem weird that these parts wouldn't give me a CEL until now?
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Old 05-19-2009, 09:33 AM   #5 (permalink)
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Quote:
Originally Posted by madmanmax3000 View Post
Okay, makes sense that the car would run richer when it knows the light is on...

What's the story with the correct non-fouler to buy? Do I want the Napa 730-2442 or the Help! 42009/42002?

Still, does it not seem weird that these parts wouldn't give me a CEL until now?
O2 sensors and high-flow cats are always weird. Some people can run them without defoulers, some need them from the moment they install the cat, others after while from installing the cat. Can't explain it.


I bought mine from strutking, but it appears he doesn't sell them anymore. Here is an angled one on ebay:

O2 SENSOR ANGLE ADAPTER EXTENSION UNIVERSAL 02 CEL:eBay Motors (item 250426150662 end time May-23-09 20:33:09 PDT)

Or a branded one, Blox:

http://www.prostreetonline.com/x/blo...eliminator.asp

Or a site (acquired from 8thcivic.com):

http://www.mechanicalo2sim.com/

Straight Sim $14 Shipped
Angled Sim $25 Shipped
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Last edited by HoRRo; 05-19-2009 at 09:36 AM.. Reason: more links Reason: more links
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Old 05-19-2009, 10:07 AM   #6 (permalink)
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had the same code on my s2k, at first i thought it was bad gas, but it came on again when I didn't tighten the gas cap past 3 clicks. Never happened again after I make sure I tighten the gas cap. Similar mods on my s2k.
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Old 05-19-2009, 11:39 AM   #7 (permalink)
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Thanks for the links Horro, I will probably end up getting one of those. However, I need the part before Friday (traveling for Mem. Day), so I will get a $5 piece and modify it in the meanwhile.

HKSSupra, I thought it was the gas cap too the last time this happened, but I've been careful since. I think I need the defouler now.

So Napa and Help! both work fine? One is not better than the other?
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