Subaru P0420 After New O2 & Catalytic Converter

SubaruOwner2 · **Joined:** Mon Mar 17, 2008 6:48 pm **Posts:** 3

Subaru Forester, I keep getting a P0420 code. I have replaced the catalytic converters and the rear oxygen sensor. Reset the code and drove 250 miles. Check engine light is back again. Where do I go from here?

Sponsored Links · **Joined:** 29 Jun 2004 08:12 pm **Posts:** N/A

Webmaster · **Posted:** Mon Mar 17, 2008 11:38 pm

Welcome! This should give a few more ideas:
search.php?keywords=p0420

Webmaster · **Posted:** Tue Mar 18, 2008 12:20 am

A few ideas:
- Use a scope to verify the downstream oxygen sensor's operation
- Check for exhaust leaks (anywhere!)
- http://www.obd-codes.com/p0420

Did you buy a quality OEM converter or a cheaper aftermarket one? The converter may be bad (again) if it's a cheap one!

STItech · **Joined:** Mon Mar 24, 2008 8:21 pm **Posts:** 10

it is possable that all you need is a ecm reflash most all dealers can do this and it should not cost any more then a hour of time (trust me i work at a subaru dealership) i my self have been reflashing for all the o2 codes any time i see a 420 code for which ther is no offical reflash and out of aprox 30+ cars only 1 has come back for a 420 code a second time good luck

SubaruOwner2 · **Joined:** Mon Mar 17, 2008 6:48 pm **Posts:** 3

I reset the codes after the 250 miles and now have over 700 miles since then without the check engine light coming on. I wish I could explain what has changed but at least things appear to be working correctly now.

timav8s · **Joined:** Fri Apr 25, 2008 8:49 am **Posts:** 1

I have a 1996 Subaru legacy Outback, 2.5. I got the Check engine light first thing yesterday morning, after filling up the gas tank the night before. I have the P0420 code. The car runs ok, although I notice a vibration while sitting at red lights in drive, that wasn't there before. Seems worse when the AC kicks on..? I thought at first the Idle was higher, causing more work on the auto trans with the brakes on, but maybe that is not the case. Anyway, I saw the previous Posts, and was wondering if anyone had any more info/suggestions. Can a tank of crappy gas sause this? P0420 can also be a vacum leak? Checking for that today. Can it be the first O2 sensor, or only the second? I replaced one of them a couple of yrs ago..forget which. Would rather not go down the cat converter trail if possible to rule everything else out first. Can I reset the code/computer simply by unplugging the battery over night? Still getting 22 -24 mpg...
all posts welcome...
Thnx.
Tim

demoman · **Joined:** Tue Apr 15, 2008 10:29 am **Posts:** 5

Hey STItech, What exactly is a reflash, Does a normal scanner do that when it eraces codes or is that a dealer only procedure?

SubaruOwner2 · **Joined:** Mon Mar 17, 2008 6:48 pm **Posts:** 3

I called the manufacture of the catalytic converter I purchased (Eastern Catalytic) and they sent me a new converter. They said they had reformulated the converter for my 2001 Subaru Forester and that should fix the problem. They also paid for the return of the one that did not work. I just had it installed and will have to report back later if it resolved the problem.

jcniest5 · **Joined:** Mon May 05, 2008 11:14 pm **Posts:** 7

SubaruOwner2 wrote:

I called the manufacture of the catalytic converter I purchased (Eastern Catalytic) and they sent me a new converter. They said they had reformulated the converter for my 2001 Subaru Forester and that should fix the problem. They also paid for the return of the one that did not work. I just had it installed and will have to report back later if it resolved the problem.

so, did the new cat fix the problem?

Subaru P0420 After New O2 & Catalytic Converter

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