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2010 XT Premium
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6 Posts
Discussion Starter · #1 ·
My CEL light came on recently , I scanned the system and found P0420 permanent code. I've read alot about it and what to do. I did replace the downstream O2 sensor about 3 months ago. The car runs perfectly. Have you had this issue and what did you do about it ?
 

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2009 Forester Base
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274 Posts
Reading just the code may not give you the full picture. If you have a relationship with a shop, ask them to put a scanner on and trend the engine diagnotics.

It maybe caused by leak in the intake manifold gasket.
 

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2010 X Limited, 2.5L NA, 4AT. Purchased as the second owner in 2020 with ~126K miles.
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It hasn't reset itself after multiple drive times so the problem appears to continue to exist. As stated, you should delve deeper into the problems that trigger P0420. Restating the obvious. :) A real time OBD2 monitor is an extremely useful tool.
 

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2011 Forester 2.5X Manual w/ Ko'2
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114 Posts
Can be a bad downpipe cat, or clogged. Mine was on my fxt 2010


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2017 Forester XT Touring
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Is there a way to bypass the cruise control being unuseable
Nope. That's one of Subaru's plans to make you fix your car instead of ignoring the code.

In my experience the P0420 code has always been fixed (4 times on three different cars, and the second time on one car was the other bank on a 3.6R) by replacing the downstream O2 sensor. Did you replace it with a good brand-name sensor or whatever you found cheap?
 

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2010 XT Premium
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Discussion Starter · #9 ·
The car runs perfectly. I just got a bottle of catalytic converter cleaner. Going to put it in today, we'll see
 

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2011 Forester 2.5X Manual w/ Ko'2
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The car runs perfectly. I just got a bottle of catalytic converter cleaner. Going to put it in today, we'll see
Mine run fine with the bad catalic also, but until you really go uphill on highway starting boosting on your way up, then you could feel it.
If catalic is not operating like it should do, no bottle cleaner of some sort will bring it back to life.
Just guessing here btw


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2007 Forester Sports XT 4EAT
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