PO136 and PO420
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This is a discussion on PO136 and PO420 within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hello all and looking for some advice.... Just picked up a low mile adult owned 02 wrx with 100k on ...

  1. #1
    Registered User tarpon1959's Avatar
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    PO136 and PO420

    Hello all and looking for some advice.... Just picked up a low mile adult owned 02 wrx with 100k on it for my son and I to work on. Did the crawl around underneath and other than the COBB cat back it was sold and appears to be stock. Very good maint records and paper to support it. Like all used cars figured on some things to sort out. Torn boot on front axle (grease on exhaust smells bad) and it threw a cel of po136 rear o2 sensor. Reset it came back so I replaced it. Local auto parts store gave me a Bosch replacement, was feeling good and then a po420 came up. Now when I look at the two sensors side by side the tip that extends into the exhaust stream is different.

    I have read the many threads on this but before I tear things apart did I introduce the po420 with the Bosch sensor? The upstream o2 sensor was replaced in August by a very reputable shop here in Portland. Not sure if there is a easy way to validate the codes.

    I did get the official Subaru shop manual to help but am looking for advice, manual can't give you that!

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  3. #2
    Registered User tarpon1959's Avatar
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    Also did some more poking around and it appears that the COBB system goes from tailpipe to Turbo...

    Here I am replying to my own thread.

  4. #3
    Moderator Donkey's Avatar
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    Exhaust FAQ: Read if you are thinking of buying one! - NASIOC

    The issue is the aftermarket high flow exhaust. The link above explains all about aftermarket exhaust on turbo Subaru's. Link below is a FAQ that pretty much covers everything. You either need an ECU retune to disable the DTC ,a mechanical fix or return the exhaust to stock.

    Unabomber's Manifesto - NASIOC
    Resident Adviser @ WTF Tuning, LLC
    2002 FORESTER S
    1998 FORESTER S




  5. #4
    Registered User tarpon1959's Avatar
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    Excellent advice, from the many posts on the subject was thinking just that after I noticed the AM down pipe. Think overall we got a good car just worried. Thanks again for the reply, I saw some of your posts and appreciate it

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