PO420 Code
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This is a discussion on PO420 Code within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hello to all. I am new at this, but I was hoping to get some good help with getting this ...

  1. #1
    Registered User rolnicktr's Avatar
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    Exclamation PO420 Code

    Hello to all.
    I am new at this, but I was hoping to get some good help with getting this stupid code off my dash. So, I have been getting this PO420 code for a few weeks now. First, I got a friend to just go ahead and reset the system to turn the light off, then it came back on a few weeks later. I have now gone the cheap route, or so I'm told, and went to purchase a new O2 sensor first before I went into thinking it was my catalytic converter. So, now that the sensor has been replaced the light went off for about 6 days. Now, the light it back on, I have gotten the engine read again and it is saying the same thing, that my catalyst efficiency is low. Well, I called a dealer today, and got some horrendous news on the price of a new catalytic converter plus labor....it was goddamn ridiculous. But anyways, I was wondering if anyone knew the exact part number or anywhere else to find the part so I can get someone to fix it for a lot less money. Also, I have been reading about this code for the last hour or so online, and it seems as though a lot of people have had problems with their subie's having this code go off and it not going away even after replacing the catalytic converter. PLEASE HELP ME!!! I AM SOOO CONFUSED!
    -Tessa

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  3. #2
    He simply abides. SD_GR's Avatar
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    The price of a catcon is not relevant right now.

    What year is the car?

    Is the car modified? If so, how? If not, see below:

    How many miles on the car?

    What state is the car located in?

    What does the owner's manual state about the EMISSIONS warranty for that state? Not the driveline or bumper to bumper or anything else -- the emissions warranty?
    WRX Info Links, Courtesy TheJ
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  4. #3
    The Default One SeattleJeremy's Avatar
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    Quote Originally Posted by rolnicktr View Post
    I have now gone the cheap route, or so I'm told, and went to purchase a new O2 sensor first before I went into thinking it was my catalytic converter.
    I hate to tell you this, but buying a new O2 sensor was not the cheap route.

    Does your car have all the stock cats? It sounds like you may be missing one or more.
    3 cat's on 02-05 WRX's
    2 cat's on 06+ WRX's, and 04+ STI's.

  5. #4
    Registered User rolnicktr's Avatar
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    Po420

    I have a 2002 Subaru impreza2.5RS. It is not modified. There are 94,000 miles on the car. The car is registered in MD. The only things that I have done to the car are basic maintenance. I am pretty sure MD has some emissions complications, but underneath the hood it says the catalyst system is set to California specifications for emissions. I am not exactly sure what that means, but I can get back to you on it if you don't know.

  6. #5
    He simply abides. SD_GR's Avatar
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    OK with that mileage you are unlikely to still be under emissions warranty. I'd suspect the wiring to the sensor before suspecting the sensor itself. If the wiring is OK then a new sensor ought to fix the problem IMO.
    WRX Info Links, Courtesy TheJ
    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
    I lied. I cheated. I bribed men to cover the crimes of other men. I am an accessory to murder. But the most damning thing of all... I think I can live with it. And if I had to do it all over again - I would. Benjamin Sisko
    DISCLAIMER: Opinions expressed are the author's alone and are inherently worthless.

  7. #6
    Registered User rolnicktr's Avatar
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    I have already replaced the bank-one sensor-one in my car. Which O2 sensor are you speaking of? The one that I replaced is located near the catcon and the transmission. I purchased the O2 sensor and then a friend told me it was the wrong one, so I got a different one, and then a mechanic told me to go get the one I had in the first place. So, I definitely replaced only the front sensor not the back one. I am pretty sure all the wire connects were A-okay though.

  8. #7
    He simply abides. SD_GR's Avatar
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    Since your car is not a turbo I am afraid I may confuse you; sorry if that's the case. The rear O2 sensor (unless turbo/nonturbo differences are confusing me) is the one near the catcon and the one that would cause the PO420. The front O2 sensor, at least on my car, is closer to the motor than to the rear catcon. From what you've written, it seems you've actually replaced the rear sensor. This should be correct.
    WRX Info Links, Courtesy TheJ
    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
    I lied. I cheated. I bribed men to cover the crimes of other men. I am an accessory to murder. But the most damning thing of all... I think I can live with it. And if I had to do it all over again - I would. Benjamin Sisko
    DISCLAIMER: Opinions expressed are the author's alone and are inherently worthless.

  9. #8
    Registered User rolnicktr's Avatar
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    Well, hmmm....I am pretty sure I understand now, and I have replaced the one near the engine, does that mean I should replace the other one in the rear?

  10. #9
    He simply abides. SD_GR's Avatar
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    If you have no CEL, the problem is over no matter how confused I may be.
    WRX Info Links, Courtesy TheJ
    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
    I lied. I cheated. I bribed men to cover the crimes of other men. I am an accessory to murder. But the most damning thing of all... I think I can live with it. And if I had to do it all over again - I would. Benjamin Sisko
    DISCLAIMER: Opinions expressed are the author's alone and are inherently worthless.

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