2003 WRX - P0420 Code and Exhaust Noise After MAF Replacement
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This is a discussion on 2003 WRX - P0420 Code and Exhaust Noise After MAF Replacement within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hi guys, I've got a 2003 WRX with 92K miles and a 100% stock exhaust system. I had my vehicle ...

  1. #1
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    2003 WRX - P0420 Code and Exhaust Noise After MAF Replacement

    Hi guys,

    I've got a 2003 WRX with 92K miles and a 100% stock exhaust system. I had my vehicle diagnosed by a shop after it deadlined on the highway recently. The shop told me my MAF failed and replaced it. After getting the car back I noticed that the vehicle sounds louder at idle, but it is not idling high. After driving about 10-15 miles I got the Cat Converter efficiency code (P0420). I cleared it only to have it return 50 miles later.

    Any suggestions on how to approach this? I've performed a visual inspection of the exhaust system and from the external view nothing appears to be incorrectly installed/missing. Do I need to pull the MAF out and inspect it?

    Thanks!

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  3. #2
    He simply abides. SD_GR's Avatar
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    I don't think the MAF would be giving you a PO420 frankly. Best bet is to take it back to the shop at this point. I'd check the wiring to the O2 sensor for a short, fault, or disconnected clip first though.
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    Ok, sounds like a good place to start. In your experience, can a missing/damaged/failing 02 sensor cause an increase in exhaust noise? I would almost think there would have to be a corrosion hole, failing, or incorrectly installed seal to cause that.

  5. #4
    He simply abides. SD_GR's Avatar
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    Yes a hole or leak would do it.
    WRX Info Links, Courtesy TheJ
    Man is a brute.... If you're cruel to him, he respects and fears you. If you're kind to him, he plucks your eyes out. Alexis Zorbas
    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.

  6. #5
    Moderator Donkey's Avatar
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    The P0420 code is for the rear o2 sensor. Free flowing exhaust with no mechanical DTC fix or engine management will cause the code as will a failing sensor or leaky exhaust.


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