PO420 driving me nuts
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This is a discussion on PO420 driving me nuts within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; new to the forum, but have searched it many times. most recent PO420 cel. 2004 wrx no mods, 50K miles ...

  1. #1
    Registered User tripwr1964's Avatar
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    Aug 2010

    Question PO420 driving me nuts

    new to the forum, but have searched it many times. most recent PO420 cel.

    2004 wrx no mods, 50K miles
    replaced both O2 sensors with oem type bosch. PO420
    dealer replaced cat. PO420
    mechanical "fix" http://forums.nasioc.com/forums/showthread.php?t=609462. PO420
    dealer tells me he can't do anything further till i put the original oem sensors back in (not sure what that means).

    i don't hear any exhaust leaks, but doesn't mean i don't have any...

    not sure what to try next.

    thks, tim
    Last edited by tripwr1964; 08-23-2010 at 03:50 PM.

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  3. #2
    Registered User wo^tron's Avatar
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    Jun 2010
    Naples, FL
    for upstream O2 sensors you can only have an OEM replacement anything else will freak the car out. It has to be ordered from a dealer. Pretty sure that's the problem.

    I had the same thig with my STi, I got an upstream o2 sensor from Advance (Denso and everything) and it threw my car into limp mode with baaad washdown and I had raw gas pouring out the back. I went and replaced it right away but my oil was still ruined. So you might want to check that too
    Last edited by wo^tron; 08-23-2010 at 04:49 PM.
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  4. #3
    Registered User tripwr1964's Avatar
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    Aug 2010

    bosch part numbers

    i installed 15537 front and 13538 rear.
    this is the second front sensor. installed first 15537 ~1.5yrs ago. everything was fine for that period of time, till now.

    anyone know the subaru part number?
    '04 WRX (new school)
    '64 GTO (old school)

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  6. #4
    Good news, everyone! xxxxxxxAnub1s's Avatar
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    22690AA520 is the number for the rear O2 sensor.

    You may want to check the wiring to the sensor and down the line a ways, make sure there are no shorts in it.
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