check engine light po171
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This is a discussion on check engine light po171 within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; So my check engine light came on and this is the code that my Cobb access port gave me po171. ...

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    Registered User bradsorensen's Avatar
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    check engine light po171

    So my check engine light came on and this is the code that my Cobb access port gave me po171.
    po171 in my Cobb accses port manual means too lean. I have a 2005 wrx with 56k and here is my list of mods.
    need some help on where to start.


    2005 STI VF39 turbo, ported and polished (bracket to run EWG, IWG is not welded)
    Tial 38mm external wastegate (silver, atmospheric dump tube)
    ultimate racing EWG uppipe
    JDM STI 565cc pink injectors (GBOD deleted)
    Walbro 255Lph fuel pump
    NGK one-step colder copper spark plugs
    2005 STI top mount intercooler w/stiBPV
    APS top mount intercooler splitter
    APS turbo inlet pipe
    APS 65mm cold air intake (with K&N C.A.R.B sticker)
    APS TGV deletes
    Hondata intake manifold heatshield
    Helix 3" downpipe (catless)
    Boria XR-1 catback exhaust (full 3" catless)
    Synic Motorsports equal-length header (wrapped)
    Koyorad aluminum radiator
    Prodrive boost control solenoid
    AEM injection kit (tuned for 50% methanol by volumn failsafes wired-in)
    Perrin crank pulley
    Ceramic-coated OEM turbo heatshield
    Sun Hyper Voltage System GT and Hyper Ground System
    Paranoid Fabrication grounding kit
    COBB AccessPORT version 1
    Tunedf by Jon Drenas (of COBB tuning SoCal)


    Merry Christmas everyone love you guys!

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    Registered User bradsorensen's Avatar
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    bupp

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    He simply abides. SD_GR's Avatar
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    Clean the MAF. Search "po171" for more info.
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    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.

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    Registered User bradsorensen's Avatar
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    so i cleand the maf and the cel turned of this morning! so if i continue to have this problem should i replace the maf sensor. o and thank for your help

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    Registered User bradsorensen's Avatar
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    bupp

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    He simply abides. SD_GR's Avatar
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    No. The MAF works. It's dirty likely because your intake is not as good as the authentic Subaru intake at doing what an intake is intended to do -- filter dirt. You've gone another direction; power. I simply think you're getting dirt on the MAF. Buy a MAF cleaner and use it periodically I guess.

    If in the future cleaning the MAF does not correct the issue, suspect something else: Check FPR reference, vacuum leaks, boost leaks. MAF harness must face forward. Check wiring, intake tract.

    I misread your response a bit ago; sorry.
    Last edited by SD_GR; 12-23-2011 at 05:10 PM.
    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.

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    Registered User bradsorensen's Avatar
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    thats cool im willing to do whatever i need to correct this issue

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    Moderator Donkey's Avatar
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    Registered User bradsorensen's Avatar
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    thank you donkey lots of go info and i will check it all merry Christmas to everyone in my Subaru family!

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    Registered User bradsorensen's Avatar
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    CirrusWRX
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    P0171 CEL Thread - Everything you ever wanted to know?
    More of an informational post than anything else. PAWRX on the boards here recently went through hell (and $$$) trying to diagnose his P0171 - Fuel trim malfunction (A/F too lean) CEL after de-modding from ~Stage 4 setup. With his permission, I'm going to post what he (and I) went through in addition to the stuff I dug up on NASIOC, i-club, ClubWRX, WRXHackers, ScoobyNet, and Google. I will try and list things in the most appropriate order of "what to check first." I'm probably going to miss some things, so please clarify if you have any experiences that contradict what he/we tried, or if I'm flat out wrong about anything. Without further adieu, the

    PAWRX & CirrusWRX guide to troubleshooting a P0171 CEL code on a 2002/2003 WRX

    First disclaimer: As with any troubleshooting, if you get this code after tinkering with something on your car, chances are the tinkering caused the code! Always look to what MOST RECENTLY changed (which can mean: installed, uninstalled, modified, etc...) when troubleshooting, no matter how remote the possibility may seem.

    1. Cold air intakes. Just as the name of the CEL suggests, the ECU is sensing a lean condition. As anybody with half a search function will find, many CAI's for the WRX will cause a lean condition due in part to either relocation of the MAF, a differently sized diameter of piping, or purely increased flow of air which is not correctly compensated for. Many people who get this code get it shortly (or instantly) after installing a CAI. The CAI would be great first place to start, especially if you recently added one.

    2. Stock airbox not sealed. Assuming you have a stock airbox, check the connections and tabs around the airbox itself. Many times, people think they "seal" the airbox, but don't actually have the top and bottom parts aligned correctly resulting in a leak. Check to make sure the air filter (esp. if recently replaced) is sitting in the right spot and the clamps are tight and everything is lined up properly.

    3. Hose leaks, generic air leaks. Mostly in and around the intercooler, turbo, BOV, vaccum lines, turbo, etc... There is a vaccum hose coming out of a nipple on the right side of the BOV on the IC; the return/recirc. line runs off of the BOV under neath the IC to the intake. It gets pulled off easily if you remove your IC without disconnecting the BOV. There are some vaccum line connections on the turbo inlet hose. The Samco turbo inlet hose does not fit 100% perfect - there could be a small leak or tear. Check the turbo outlet, and Y connections on the IC. Check for a tear or leak or loose clamp on any replacement hoses. Check all hoses in any area where you were recently working on something. Boost gauge installation or UNinstallation. IC installation, FMIC installation/uninstallation. All those hoses need to be securely connected and routed to the appropriate places! If necessary, find a buddy with a WRX, park them side by side and trace all the lines. Chances are you would would also notice some sort of boost fluctuation/abnormality if there were a leak, but this is not always the case.

    4. Fuel pressure regulator. According to the factory service manual and suby techs, the most common problem with the FPR is the vacuum connection to the intake manifold (either cracks in the hose where it makes a sharp bend, or a leaking connection.)
    Occasionally, the fuel pressure regulator reference line will pop off or is accidentally left off when working on or around items located near the passenger side fuel rail. (ie. injectors, spark plugs, reaching for something...) This is a serious mess up, but one that is easily corrected.

    5. Check all ground connections. While you can certainly verifiy all of them, one person mentioned specifically being able to fix their problem by checking their grounds. They discovered that the ground wire on the drivers side of the intake manifold (the bolt) was loose and was causing the P0171. Make sure that bolt, and all others, for that matter are tight. This one is somewhat random, but it's so easy to check.

    6. Injector problems. I came across two people who posted about a P0171 after removing AFTERMARKET injectors and going back to stock injectors. In both cases, the stock injectors had been sitting in a box inside their houses for over a year. It was believed that the fuel had crystalized and caused a blockage of some sort on one or more of the injectors. This could potentially happen with ANY used injector that has sat for a long time. In both cases, the individuals used fuel system cleaner (is it called "heet"?) and the P0171 went away.

    7. MAF sensor gone bad/dirty. This is an easy one to check if you can find somebody willing to swap MAF's for a day or two. The MAF looked good on PAWRX's car, but we decided to swap it with mine just for gits and shiggles. The process to do this is so simple, requiring a single clip and two screws. Swap MAF's with a local (and friendly) WRX buddy, reset your ECU and drive for a day or two. If you get your P0171 again, the MAF was not it. If you go CEL free, and even better, if the OTHER person gets a P0171, then you found your culprit. Either clean the old MAF or shell out the cash for a new one. In our case, PAWRX got his CEL the same way as always after we swapped MAF sensors.

    8. Front oxygen (o2) sensor, located in passenger side exh. manifold gone bad. This was the final solution to PAWRX's problem. Again, we "swapped" (I didn't actually install his o2 in my car) and his problem disappeared. His o2 looked "worn" but not bad by any means. His experience with the P0171 basically had the car run fine for the first 10-15 miles until N.O.T. Then, after power cycling (shut off car for a minute, turn it back on) and driving at a constant highway cruise for a few minutes, the CEL would come back on. After checking #1-#7 above, we were left with swapping the oxygen sensor, and that was the ticket in our case. After trying a few cruises and power cycles with no CEL, he ordered a new sensor from Subaru. While waiting for the nwe sensor to arrive, he reinstalled the "bad" o2 sensor in his car and drove home. Upon starting up the next time, he got the CEL. Since installing the NEW o2 sensor 3 days ago, no CEL.

    In his case, with the "bad" o2 sensor, the CEL would disappear after resetting the ECU, but would come back on after shutting the car off and cruising on the highway for a few minutes. When the CEL was on, the car would run extremely rich and dump fuel like crazy. I think he said he would see anywhere from 325-350 miles to a tank with conservative driving, and he was seeing something like 200-250 miles to the tank when the CEL was on.

    9. You are truly running rich/lean and the ECU is not happy, thus the code is legitimate
    There have been a few cases, noted below, when doing some type of tuning either via UTEC or a tuner with ECUTEK that results in the parameters being off scale and thus throwing the P0171. Perhaps you are truly running a bit too lean for the ECU's tastes and either the parameters for detecting the P0171 are not wide enough or your tuning is off. In the case of ECUTEK, it seems some people with DeltaDash can make some small adjustments in some cases, other cases might result in needing a professional retune (UTEC) or reflash (ECUTEK).

    10. Dirty Idle Air Control Valve (IACV) - clean it out with carb cleaner or equivalent, however be sure to do this when the engine is cold so as to not cause deformation of the gasket. If you do happen to cause it to deform, a new one is about $8 from a Subaru dealership. Thanks samneric!

    This is not meant to be an all-inclusive, be-all-end-all guide to the P0171, but it should be a good help for those experiencing it and banging their heads against the wall. Obviously, use your wits about you. If you have a CEL and get the code pulled, and you have 6 other codes thrown along with the P0171, you have OTHER problems that need serious attention. This is meant more for the people who randomly get a P0171 and can't figure out what they should do. PAWRX went through a lot of hell, money and effort to troubleshoot his car, and I have to be honest and say that I never thought the o2 sensor could cause something like this. Upon my research of the code, it appeared that #1-#6 were the most common reasons for getting it, but we both felt it would be worthwhile to post our experience in this matter for the good of the community. Again, any additions/corrections, please let me know and I'll edit anything ASAP.

    Thanks - CirrusWRX & PAWRX


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    Last edited by CirrusWRX; 12-22-2004 at 02:28 PM.

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    Registered User bradsorensen's Avatar
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    So iv come to the conclusion that my po171 problem seems to be most likely #8 on the list. I have all the same problems so i ordered the o2 sensor and it will be here in the morning, and i encountered a new problem when changing out a bad head light a mouse or rat had made a nest on top of my alternator.Attachment 101342 so to my knowledge this is heat tape for my exhaust or for some other heat sensitive area. I work in snohomish next to a river so im thinking that's where the mouse or rat came from.

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    He simply abides. SD_GR's Avatar
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    I can't comment on the rodent; however, with an "open" air filter I would suspect dirt on the MAF far before suspecting the actual O2 sensor personally. As you hold the MAF, the visible "sensor" I think measures temp (right, anyone?) and the actual air flow sensor is buried in the staff of the MAF. If you're getting another PO171, give the cleaning another go, and this time also clean the filter itself, the intake on the inside as much as possible, and check thoroughly for vacuum and/or boost leaks. All this is frustrating but free. I'd look at the actual sensor last, and beg/borrow/steal a known working sensor from another Subaru guy just to test first. Just my take though, and I'm not a mechanic.
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    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.

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    Registered User bradsorensen's Avatar
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    sorry guys forgot to mention i cleaned the MAF this week total soked it in MAF cleaner with no luck.

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    He simply abides. SD_GR's Avatar
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    OK so your choices are now fitting the correct intake if possible and/or searching for vacuum and boost leaks before throwing parts at it etc. Sorry to hear. Courage, and good luck.
    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.

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    Registered User bradsorensen's Avatar
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    thank you man i will keep you up to date on progress. the weird thing is the car runs idles and turbo boost is great. the only difference i can see is my gas mileage.

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