oil change and catalytic converter code P0420

I drive a Subaru Forester 2001. I just made an oil change and converted from synthetic oil back to conventional since I don't feel seeing any benefits from synthetic oil. A couple weeks after that, CEL comes on and the code read as P0420 related to catalytic converter. I'm wondering whether it could be related to the oil change swinging

between synthetic and conventional oil? Or it could just be just coincidence......

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I'd say coincidence. Um....did you do any other service at the time?

Clear the code, if it comes back immediately and the car runs poorly, it could mean the front O2 sensor is bad or the catalytic converter is bad. If you can clear it and it comes back in a few hours or days - and that cycle can be repeated. Most likely the front O2 sensor is 'lazy'. A good mechanic can scope the output from the sensor and determine its condition. DIYers usually just swap it out hoping that fixes the 0420 code. It often does.

Carl

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Yep. Had the same on 2002 Forester, changing front oxygen sensor removed the CEL and periodic hesitation.

DK

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Thanks a lot for sharing! How much it took you for replacing the front O2 sensor?

On Oct 11, 12:23 pm, snipped-for-privacy@no.email.thankstospam.net (DK) wrote:

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Vague memories: $73 OEM sensor + $25 for 15 minutes of actual work charged. That's at an independent mechanics. Dealer would have charged a whole one hour of labour. To be honest, once I saw what was changed and where, I could have ordered part online for about 30% less after shipping and change it myself. Seems really trivial even for a hardware-challenged guy like me.

DK

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Go have a look at the Catalytic converter. It may have a hole in it. LIke mine.

You live in the snow belt?

Oil change may just be a red herring.

p0420 is a frequent visitor for me. BP gas seems to make it happy and stay away for longer, crazy as it sounds. We'll see as we move into winter gas.

-- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA

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On Oct 11, 5:29 pm, snipped-for-privacy@toddh.net (Todd H.) wrote:

I live in North Cal. Oil change sounds like a red herring that I agree. Another coincidence is that I had to jump the battery after I forgot to turn off a ceiling light and didn't drive it for a week. I have only driven this Forester infrequently in last few months, about once a week. It still gives me trouble :( I have changed a knock sensor three years ago. Really start to doubt Subaru's quality, at least for 2001 model...

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In all fairness, it's 8+ years old (I don't recall you mentioning the mileage) and infrequent driving is considered 'extreme service'. Many cars would give you some trouble in similar situation.

If you can, have Autozone clear the codes, drive it, and see how quickly any codes return. Give it a few drive cycles.

Carl

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