2002 Subaru Forester P0420 Code

2002 ALL OTHER MAKES ALL OTHER MODELS
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FRANK FLORENCE
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2002 Forester, 108,000 miles.
Check engine light first came on after improperly replacing gas cap. Now comes on intermittently even when cap on straight, although currently off. Computer diagnostics indicated catalytic converter ($1100!) is faulty (tested when light off). Would like to change (or have changed) emissions filters to guarantee these aren't part of the problem. What should be replaced?
Jan 10, 2007 at 1:09 AM
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SERVICE WRITER
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Hi Frank,
Give us the code number pulled.
Has this been diagnosed or just presumed?
Jan 10, 2007 at 8:49 AM
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FRANK FLORENCE
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Service Writer,

The listed code is P0420 - cat converter failure.

When I was given this report, I asked what was fouling the converter and had the mechanic looked at the emissions system or filters. Also why was I getting this code if the check engine light was currently off? Did this mean that there had be an O2 problem in the past or was there currently a problem?

The reply I got was "The computer says you need a new cat convertor."

Some mechanic.
Jan 11, 2007 at 3:02 AM
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SERVICE WRITER
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Catalyst System Efficiency Below Threshold (Bank 1)
This may not be a cat! Dog either:)

According to the info I have, the code needs to be cleared. and then a drive cycle performed twice.

Subaru says to not diagnose this code if it is alone.

After codes are cleared, turn the ignition key to on, but not cranking for 3 seconds to initialize the idle speed control motor.

The drive cycle involves driving for 50 mph, then stopping then car and idling for one minute. Then repeat the cycle.
Jan 11, 2007 at 10:15 AM
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FRANK FLORENCE
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Useful information! Thanks.

However, I don't know how to clear the code. Is this something I can do? Or would another service center be able to do this?

I have no confidence in the Subaru shop that gave me the initial estimate so I'm not excited about going back to them. I got the feeling that all they really wanted to do was sell me parts (versus solve a problem.)
Jan 11, 2007 at 2:35 PM
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SERVICE WRITER
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I don't know how other than using a scanner. I do know that autozone has done this for free in our neck of the woods. An independent shop can do this. I would send you to a shop I know but that would be geographically challenged :)

What I suggest if you can't find one through a source you trust, is to contact the local snap-on dealer tool dealer, he knows the good shops and could refer you.

www.snapon.com

Good luck :)
Jan 11, 2007 at 7:06 PM
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FRANK FLORENCE
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Great. Thanks again for the help.
Jan 12, 2007 at 12:25 AM
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Suggested Repair

Do not replace the catalytic converter based on P0420 alone. Have the code cleared with a scan tool, turn the key on without cranking for three seconds to initialize idle speed control, then complete the specified drive cycle twice before further diagnosis. An independent shop or parts store can often clear the code.

Conversation Summary

The owner of a 2002 Forester with 108,000 miles reported an intermittent check engine light after a gas-cap issue and was quoted for a catalytic converter after a P0420 reading, even though the light was off. The expert said Subaru guidance is not to diagnose P0420 when it is the only code. The code should be cleared, idle speed control initialized, and the drive cycle performed twice before condemning the converter. The owner was advised that a scan tool is needed and that an independent shop or parts store may clear it.

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