02 wrx CEL help
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This is a discussion on 02 wrx CEL help within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hy everyone, I'm new with subbies so please help me. I have a n 02 wrx with 142k on it. ...

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    02 wrx CEL help

    Hy everyone, I'm new with subbies so please help me. I have a n 02 wrx with 142k on it. It is a manual an all stock besides an aem CAI. I pulled the codes with my code reader and it came up with P0171 and code P0420. I'm assuming some of you know what these codes mean( lean mixture on bank 1, and catalytic converter below threshold.) do these codes go together? Do you think both the 02 sensors are bad? Where should I start? All the plumbing on the CIA is tight. Please help, thanks!

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    and the Funky Bunch Calvinball's Avatar
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    Are you the original owner, or did you just buy it?

    If just bought, are you sure the downpipe is stock?
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    Pro Manscaper Mikie13's Avatar
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    Does sound like bad o2 sensors to me.

    Agreed with the downpipe question Will above has posed...
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    and the Funky Bunch Calvinball's Avatar
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    Quote Originally Posted by Mikie13 View Post
    Does sound like bad o2 sensors to me.

    Agreed with the downpipe question Will above has posed...
    And I agree with 02 sensor, but I figured it's easier to check the downpipe first, assuming the car was purchased used
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    Quote Originally Posted by Calvinball View Post
    Are you the original owner, or did you just buy it?

    If just bought, are you sure the downpipe is stock?
    Just bought it ( got a good deal)
    Im pretty sure the down pipe is stock. Looks like a cat right after the turbo and it has metal heat shields covering it.
    Also the thing runs awesome if that helps.
    So you think both the 02 sensors are shot?

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    and the Funky Bunch Calvinball's Avatar
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    Quote Originally Posted by USMC View Post
    Just bought it ( got a good deal)
    Im pretty sure the down pipe is stock. Looks like a cat right after the turbo and it has metal heat shields covering it.
    Also the thing runs awesome if that helps.
    So you think both the 02 sensors are shot?
    If the downpipe is stock, there's some possibilities. One or both sensors could be bad, any shop can test those for you pretty easily. It could also be the catalytic converter itself.
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    Quote Originally Posted by Calvinball View Post
    If the downpipe is stock, there's some possibilities. One or both sensors could be bad, any shop can test those for you pretty easily. It could also be the catalytic converter itself.
    Do you test the voltage coming out of the sensors? I can test them myself with a voltmeter. Do you know what the voltage that they are suppossed to put off when theyre good or bad?

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    and the Funky Bunch Calvinball's Avatar
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    Quote Originally Posted by USMC View Post
    Do you test the voltage coming out of the sensors? I can test them myself with a voltmeter. Do you know what the voltage that they are suppossed to put off when theyre good or bad?
    Yes, you can test it yourself then. I believe the important thing is not so much the voltage, but that they are fluctuating. They should not read steady. Google time...

    Bam. Here ya go: How to Test an O2 Sensor | eHow.com
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    PO171 indicates a bad O2 sensor but that is last on the list of things I'd suspect causing the CEL. I'd troubleshoot PO171 fully first, leaving the O2 sensor for last. You already know the intake is incorrect. Did you clean the MAF? Please search for troubleshooting PO171, there is a whole list of things to do posted.

    PO420 indicates a bad O2 sensor also but I'd suspect wiring first, or an aftermarket or absent cat etc.
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    Moderator Donkey's Avatar
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    The P0171 can also be caused by an aftermarket air intake that is skewing the MAF reading. The P0420,even with an aftermarket highflow catted downpipe,can still be triggered.
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