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Thread: Persistent P0171 and P0174 codes

  1. #1
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    Persistent P0171 and P0174 codes

    2001 M54b25

    I keep getting the typical lean codes. Alternates between the two but If I wait long enough, both will be up. I try to clear codes to single out the instance. Its definitely intermittent. I may get it once a week and if I clear I may not see it for another week. So its not perpetually running lean, unless a certain check has to cross for it to detect lean (30 minutes or run time, or whatever as an example)

    I have replaced both boots. I have replaced the disa o-ring. CCV was replaced 2014 but I will look back to this as a final look (probably delete CCV). I have also replaced a vacuum line that ran off the elbow of the intake boot.

    What's left... the PO installed a K&N filter. Im going to try and re-oil it but I have a used stock airbox on the way. The used airbox also has an MAF so I can try and swap that out too.

    Am I mising anything outside of just buying 2 more O2 sensors?
    Last edited by jaredmac11; 06-09-2018 at 09:44 AM.

  2. #2
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    Also remember the small vent hoses at the end underneath the intake manifold that supply vacuum to the secondary air valve and there is a vacuum cap there also.

  3. #3
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    How about a smoke test?


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  4. #4
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    Quote Originally Posted by edjack View Post
    How about a smoke test?
    Good idea, I think its that time...



    Quote Originally Posted by jclausen View Post
    Also remember the small vent hoses at the end underneath the intake manifold that supply vacuum to the secondary air valve and there is a vacuum cap there also.
    I didnt think of those. Not too familiar with this engine. Are you referring to here?: http://www.realoem.com/bmw/enUS/show...diagId=11_7539

  5. #5
    geargrinder's Avatar
    geargrinder is offline Having No Trouble Here BMW CCA Member
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    I think youre going down the right road. Both/alternating banks tends to confirm its upstream / intake side, vs O2's where normally you'll get one going out first, instead of aging perfectly symmetrically. Keep looking intake, if PO did a K&N who knows what other little mess he might have made during the conversion.

    On M54's don't forget possiblity of cracked plastic valve covers. That won't (shouldn't) generally show up w smoke test because of the check valve nature of the CCV.
    2003 M3CicM6 TiAg
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  6. #6
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    Well unfortunately it wasnt the K&N filter. The code is back.

    Could someone help me identify some hoses that I should look at? I want to put aside the CCV for now. It was replaced about 5 years ago and Im going to run off the assumption its still good since it passes visual inspection. I took a look at DISA and while Im no expert, the flap seemed to have a strong spring and closed ok. so Im assuming there's a rubber hose cracking somewhere. I heard there was a hose behind the intake that is usually suspect? I dont wanna poke around there too much until I have an idea what Im looking for, making things worse.

    Should I just replace all the hoses on this diagram:
    http://www.realoem.com/bmw/enUS/show...diagId=11_7539
    and this diagram:
    http://www.realoem.com/bmw/enUS/show...diagId=11_7622

    Or are some of these pretty inaccessible? If anyone has any guidance I could use it.

    edit: Oh boy, these are genuine BMW part only hoses. Cant wait to drop $100+ for rubber hoses...
    Last edited by jaredmac11; 06-20-2018 at 04:25 PM.

  7. #7
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    Just a follow-up, it was the oil return hose for the CCV. An oil catch can delete would have resolved this. Didnt think a part of the CCV installed in 2014 would fail in 3 years but here we are!! The oil return hose had a protective mesh around it and made it hard to find the crack. Eventually it was wide open and easy to spot. Maybe the hose was deemed 'fine' and not replaced by the mechanic. Goes to show unless you did it yourself, question everything

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