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Registered
2002 forester L
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26 Posts
Discussion Starter #1
If I am in the begininging of possibly needing a replacement for my catalytic converter about how many miles before I might need one? I am at about 120,000 now.
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,931 Posts
It kinda depends on if it gets killed by a failing front O2 sensor. Why do you think your CAT needs replacing? :confused:

Bobby...

My MODding Journal
 

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Registered
2002 forester L
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26 Posts
Discussion Starter #3
well

The P0420 showed up and when I took it to my mechanic he said down the road I would need a new catalytic converter. He said use it till I have to get it. I took a trip to Santa Fe from Norman Oklahoma and I did not have any issues. So I don't know?
 

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Registered
2011 Forester X AT
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4,235 Posts
You can typically drive on a P0420 indefinitely unless your state emissions control tests you, or the cat is so clogged that it produces enough restriction....note if it gets clogged enough you may burn a valve. How long you have depends on if you're burning oil or if you're running rich. It could simply be a leak in the exhaust not allowing the cat get up to its efficient temp, but that's not usually the case.


If you replace I highly recommend going with a direct bolt on magnaflow and replacing your O2 sensors.

The cat on my 2002 S went at 81,000 miles. I've been told this is typical for subaru cats. I guess consider yourself lucky it lasted till 120,000.
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,931 Posts
The P0420 showed up and when I took it to my mechanic he said down the road I would need a new catalytic converter. He said use it till I have to get it. I took a trip to Santa Fe from Norman Oklahoma and I did not have any issues. So I don't know?
I have a few questions.
  • How has the engine been running? Any hesitation or backfires?
  • How's the gas mileage been? Normal, or less than before?
  • Is the exhaust tip overly sooty?
After you answer the questions, I'll give you my guess as to what the problem could be. :wink:

Bobbby...

My MODding Journal
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,931 Posts
My first choice was a failing front O2 sensor, but with your answers, not so much now. :smile:

Assuming the front O2 sensor is operating correctly, there are a few possible causes.
  • Rusted thru exhaust pipe or fitting allowing air to enter the exhaust ahead of the CAT or rear O2 sensor.
  • Failing CAT.
  • Failing rear O2 sensor.
Of course you could always try the $5 fix. :wink:

Bobby...

My MODding Journal
 

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Registered
2005 forester xt
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243 Posts
your mechanic should have been able to easily diagnois this.
its not always the convertor.
front (a/f)(o2)sensor
convertor
rear o2 are the items to cause this.
all your mechanic has to do is graph the front and rear o2 sensors with his scanner to find the cause.
just dont want you to see you replace parts that are not needed.
 

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Premium Member
2007 Forester XT Sport
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3,082 Posts
Reading this now, I should have sent you over to our local forum. The dealership in Norman is not known for its efficiency, cost effectiveness or anything else.
 
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