Sorry another P0420 question
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This is a discussion on Sorry another P0420 question within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; And yes I did search the forums but couldn't find the answer I need. I just bought my '03 on ...

  1. #1
    Registered User streetfighterkz's Avatar
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    Sorry another P0420 question

    And yes I did search the forums but couldn't find the answer I need.

    I just bought my '03 on Friday. It has ~87K, and as far as I know it's completely stock. I've driven it about 300 miles and my CEL just came on. I had it checked and of course it was the notorious P0420 code.

    So I have three questions.
    1) Can an all stock car with 87K have a bad O2 sensor already?
    1) I bought the car "As Is" from a Ford dealership. What's the chances of me getting them to fix it.
    2) Since the sensors seem to be really expensive, how do I know if I need to replace the front or rear sensor?

    Thanks for the help.

    Later, Doug

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  3. #2
    Registered User 06WRXturbo's Avatar
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    P0420 is a catalyst inefficiency code. It is most likely going to be the catalytic converters. Check for small exhaust leaks. If it is an 02 sensor, they can be anywhere from $150-$250 (OEM, aftermarket may be cheaper). it's the labor that costs the most. Expect at least 1.5-2.0 hours labor (at 80-100/hr) + parts if you don't do it yourself. At 87K you have exceeded the federal cat warranty of 8 years/80K miles. Cat prices have recently come down but $900-$1200+ factory cats are not uncommon.
    Last edited by 06WRXturbo; 12-09-2008 at 08:16 PM.

  4. #3
    Registered User ArchangelF16's Avatar
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    Other option is you could buy an aftermarket downpipe and a Cobb AP, then flash stage 2. More power and no code.

    Might need to either gut or replace the uppipe though w/ the bugeye
    2004 White WRX (R.I.P.)
    2006 White TR replacement
    1998 V5 Grey STi

  5. #4
    Registered User Drifting02WRX's Avatar
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    honestly, if it takes you more than 30min. to change it out yourself something is wrong. the upstream is a little tight to get to, but it still isnt worth paying someone else to do it... and i work at a suby dealorship...
    member of teh sex... i mean bugeye mafia (#92)

  6. #5
    Registered User streetfighterkz's Avatar
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    I did some searching and it seems like some guys are installing the Spark Plug Non-Foulers on the rear O2 sensor. They say it tricks the O2 sensor and most of the time keeps the CEL from coming on. So my question is, if I install the non-foulers will the car run richer or leaner? Or is the rear O2 sensor not connected to the engine management system, only the emission system? Also will the P0420 code have an effect on the mpg of the car?

    Sorry for all the questions. But I just bought the car and need to pass emission testing before my 30-day tag runs out. I just want the car to run well.

    Thanks, Doug

  7. #6
    Registered User Drifting02WRX's Avatar
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    neither... all it does is pull the rear 02 out a bit so it doenst allow as much of the gasses to get to the sensor. car runs the same, but without the code.
    member of teh sex... i mean bugeye mafia (#92)

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