CEL Flashing Code 420...Help - Subaru Forester Owners Forum
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post #1 of 11 (permalink) Old 10-17-2006, 11:55 AM Thread Starter
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CEL Flashing Code 420...Help

I have a 2000 Forrester that is flashing a CEL code 420 ---inefficient catalytic converter. I just had the 60,000 mile service on it but did not replace the front 02 sensor or the rear one. The mechanic thinks it is the catalytic converter that needs to be replaced. He got the CEL light to switch off but wants to run it to see if it comes back on and then rediagnose it again. My bet is that it comes back on. What do you guys think? Is it the catalytcic converter or the O2 sensor(s) or something else? What should the next step be in your opinion?

Thanks

Tom S.
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post #2 of 11 (permalink) Old 10-17-2006, 04:07 PM
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http://ponyexpressperformance.com/wrxmileliminator.html it's a common issue with the RS and it's a quick fix. I have a new one for $15 shipped, since i sold my RS a couple of weeks ago.
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post #3 of 11 (permalink) Old 10-17-2006, 04:59 PM
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Code 420... I think it means your car is stoned. Did you, perchance, loan it to Cheech and Chong recently?

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post #4 of 11 (permalink) Old 10-17-2006, 05:15 PM
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i always thought of that way too, but it's P0420....
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post #5 of 11 (permalink) Old 10-17-2006, 06:25 PM
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Since you're under the 80k mile warranty, P0420 could mean a free replacement of your converter.

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post #6 of 11 (permalink) Old 10-17-2006, 06:36 PM
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Quote:
Originally Posted by Dan View Post
Code 420... I think it means your car is stoned. Did you, perchance, loan it to Cheech and Chong recently?
A+!

I am curious if it is an o2 sensor. I will watch and see. Do you have emmissions tests where you live?

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post #7 of 11 (permalink) Old 10-17-2006, 07:14 PM
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Yes it should be covered if it's the cat but not if it's the rear sensor which will be the one that sets this off not the front. Having the code itself does not effect the car's AF ratio like the front one. What it is, is the rear O2 sensor saying the temp of the gas coming out of the cat is out of range. That can happen if you put in an aftermarket exhaust, get that area packed with snow (depressing the temp) or the sensor being out of wack.

I have some info here on a fix if you know it's because the exhaust flow has changed due to something you did:

http://www.scoobymods.com/forums/showthread.php?t=5468

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post #8 of 11 (permalink) Old 10-18-2006, 12:31 PM Thread Starter
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Originally Posted by Roly View Post
http://ponyexpressperformance.com/wrxmileliminator.html it's a common issue with the RS and it's a quick fix. I have a new one for $15 shipped, since i sold my RS a couple of weeks ago.
Thank you. What does this thing do? Looks like it overrides the CEL. Is it difficult to install?
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post #9 of 11 (permalink) Old 10-18-2006, 12:34 PM Thread Starter
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Originally Posted by Peaty View Post
Yes it should be covered if it's the cat but not if it's the rear sensor which will be the one that sets this off not the front. Having the code itself does not effect the car's AF ratio like the front one. What it is, is the rear O2 sensor saying the temp of the gas coming out of the cat is out of range. That can happen if you put in an aftermarket exhaust, get that area packed with snow (depressing the temp) or the sensor being out of wack.

I have some info here on a fix if you know it's because the exhaust flow has changed due to something you did:

http://www.scoobymods.com/forums/showthread.php?t=5468

Thank you. The only thing I did recently was to get a 60,000 mile tune up. It happened a few weeks after that. What prompted the 60,000 mainteneance was a CEL that indicated that the 3rd cylinder was misfiring or whatever. I thought replacing the spark plug wires fixed that. It did for awhile anyway.
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post #10 of 11 (permalink) Old 10-18-2006, 12:36 PM Thread Starter
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Since you're under the 80k mile warranty, P0420 could mean a free replacement of your converter.

Thank you! I did not know the warranty was 80,000 miles. How do I determine if it the Cat or one of the sensors that is causing the problem?
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post #11 of 11 (permalink) Old 10-18-2006, 12:41 PM
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Quote:
Originally Posted by Tom S View Post
Thank you! I did not know the warranty was 80,000 miles. How do I determine if it the Cat or one of the sensors that is causing the problem?
The warranty is not a subaru thing - it's a federally mandated thing. Every car sold in the US since the mid 70s carries a 8 year/80k warranty on selected emmissions components, including the catalytic converter.

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