oil change and catalytic converter code P0420

[swzhao]

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......

 

[1 Lucky Texan]

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......

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

 

[DK]

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.

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

DK

 

[Hangaround]

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

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.

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

DK[/QUOTE]

 

[Todd H.]

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......

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.

 

[DK]

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

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

 

[Hangaround]

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.

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...

 

[1 Lucky Texan]

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...

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