PO171 system too lean (bank 1)
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This is a discussion on PO171 system too lean (bank 1) within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I was driving home from the mountain today and noticed a CEL. Turned off the car plugged in my AP ...

  1. #1
    Registered User 6waystillsunday's Avatar
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    PO171 system too lean (bank 1)

    I was driving home from the mountain today and noticed a CEL. Turned off the car plugged in my AP and found this code. I read a few posts that talked about this and what to do, But I just wanted a better opinion with the mods of my car, miles ect.

    05 wrx 27,000 miles
    Mods include:
    Aps cai
    Aps turbo back
    Cobb AP Stage 2.

    I reflashed the ecu to see if the code comes back on. And if it does what should I do?

    Thanks for your time.

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  3. #2
    He simply abides. SD_GR's Avatar
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    Check for vacuum leaks.
    Replace the factory air intake and make sure it's seated and seals correctly.
    Clean the MAF.
    Check the vacuum connection to the fuel pressure regulator.
    If all else fails, assume the CEL is actually correct and check the O2 sensor.
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  4. #3
    Registered User 6waystillsunday's Avatar
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    What is good to clean a maf sensor? I work at a dealer and have access to most zep products along with parts wash.

  5. #4
    He simply abides. SD_GR's Avatar
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    There's a dedicated MAF cleaner product made by a company I think is named CRC or something to that effect. It's in a gray/white can. I think Big Sky WRX made a "clean your MAF" thread a while back, and the product was pictured (search). Since the MAF is more of a sensitive electronic part than it is a car part, I'd only use something you know will not harm the sensor.
    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.

  6. #5
    Registered User 6waystillsunday's Avatar
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    alright, Thank you for your help.

  7. #6
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    a P0171 is normally a vacuum leak or a misfire. I would say that less than 5% of the time this code comes from a faulty o2 sensor. Check around for cracked/ loose vac lines. You could also have a misfire, although about half the time you will also get a coded misfire code (P03XX.)
    2002 SRP wrx mt sedan
    AP v2.0 stg 2

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