Car keeps throwing code
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This is a discussion on Car keeps throwing code within the Tuning: Electronic Engine Management forums, part of the Tech & Modifying & General Repairs category; I have a 02 WRX it keeps throwing the code p0171 so far I've checked for vacuum leaks, I've cleaned ...

  1. #1
    Registered User frenziedcage's Avatar
    Join Date
    May 2012

    Car keeps throwing code

    I have a 02 WRX it keeps throwing the code p0171 so far I've checked for vacuum leaks, I've cleaned my MAF sensor, I changed my O2 sensor like 4 months ago what else could it be? I'm probably gonna check my fuel pressure tomorrow could it be due to my tune? I'm running a OTS stage 2 map. My current mods are TBE, catless up pipe, turbo xs tmic, 3 port ebcs, intake, P&P heads +1mm valves. I have been running this OTS MAP with no problem for a little over a month now so not entirely sure if its to do with the tune or something else?

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  3. #2
    Registered User Obeisance's Avatar
    Join Date
    Apr 2012
    not Ann Arbor
    I suppose that if your tune was fine before, but the car is not fine now, that the tune should not be the source of your issue. I think that you're following a good route to diagnose this: I believe the system involved is the air and fuel measuring feedback loop with the ECU. You've looked for air leaks (be sure to check both the intake tract and the pre-turbo exhaust), and are checking fuel delivery next. Since you've replaced the O2 sensor, I have one more possible sensor for you to consider:

    I have not actually checked (nor do I know how) to see if the MAF can actually go bad, but according to this NASIOC thread, cleaning it may not be enough:

    Mass Air Flow Sensor (MAF) FAQ: Read as you know less than you think you do! - NASIOC

    If you cannot find evidence of a plugged injector or low fuel pressure (or missing or poor spark on one cylinder), perhaps the MAF could be the source? If you figure out a way to measure the effectiveness of the MAF, please let me know... maybe if you have a friend with a well functioning wrx, you could temporarily swap to see a difference.
    David - '05 WRX

  4. #3
    Admiral Ackbar the 1st mycologist's Avatar
    Join Date
    Oct 2005
    Late Devonian
    I Support ClubWRX
    What O2 sensor did you use. If you did not use the one from the dealer or its exact one from the manufacturer it is not fixed and must be redone.

    How did you check for vac. leaks?

    If it is not your sensor, it is most likely a leak in the intake tract after the MAF before the turbo. The stock inlet rips (often out of site on the bottom) right at the turbo often. Those clamps all have to be properly tightened. I put zip ties around all the hoses coming into that section as well. If your MAF is bad I think you get a CEL directly toward that but am really not sure. Any air that enters that section is unmetered, and the turbo is pulling it in strongly. After the turbo leaks blow air out.
    "From a little spark may burst a mighty flame." - Dante
    "The stitch is lost unless the thread is knotted." - Italian proverb

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