2001 DTC P0420 Catalyst System Efficiency Below Threshold - Subaru Outback - Subaru Outback Forums
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post #1 of 4 (permalink) Old 03-08-2009, 06:13 PM
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2001 DTC P0420 Catalyst System Efficiency Below Threshold

I have a 2001 Outback 2.5L and my check engine light is on. I checked the system with a Actron ODB II AutoScanner and it came back saying with "P0420". I looked that up in my service manual and it came back as "Catalyst System Efficiency Below Threshold. Has anyone had this problem before and what did you do to fix it? Let me know if I am in the wrong General Area for this type of question. Thanks

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post #2 of 4 (permalink) Old 03-08-2009, 07:08 PM
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PO420 is THE most common code of them all. There are literally dozens of threads on PO420. Use the search function and you'll have lots of reading.
Don't worry, 99.9% of the time it's not the catalytic convertors.

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post #3 of 4 (permalink) Old 03-08-2009, 07:17 PM
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Commonly, but not always, it's a dying O2 sensor. Front need to be Subaru, rear can be generic.

Have you tried using the Google search bar at the top of the forum?

2003 Outback 2.5 wagon: "Kaylee". 162,000 and counting.
More rust than I care to think about. And leaking head gaskets. And electrical gremlins. Still flyin'.

2002 L.L. Bean Limited 3.0 Outback wagon: "Mal". 112,000 and counting.
Plenty of battle scars and fixing up the previous owner's neglect via Project Retrograde.
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post #4 of 4 (permalink) Old 03-08-2009, 09:32 PM
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I just got the same code on my 00 today. This is the fourth or fifth time it has tripped the light. I clear it and it's gone for months. I second the weak 02 sensor but I believe another possible cause is an exhaust leak.
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