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  1. #1
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    Default Engine code p0171 = System too Lean (Bank 1)

    I have a 2004 svt and my check engine light went on yesterday my car has been idling at around 1300 rpm. It's running really rough also. It hesitates when I accelerate and is erratic when I drive slow. I think it's a bad fuel filter but I was wondering what else it could be because I plan on working on it tomorrow. Does anyone have any ideas?

    Thanks,
    Nick

  2. #2
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    check your MAF sensor. If needed, clean it with some electronics cleaner and make sure it's dry before reinstalling it. If your CEL still comes on, quite possibly might be a fuel filter issue.
    Jimel aKa ScooteR
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  3. #3
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    vacuum leak
    Stock 03 Svt Focus
    92 Mustang GT (Shell sold, Drivetrain waiting for next project)
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  4. #4
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Ok thanks. I just cleaned the MAF sensor and the light is still on. I'm changing the fuel filter now and if it's still running rough I'll check for a vacuum leak.

  5. #5
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    I had the same exact problem. I cleaned the MAF and then changed the fuel filter. The light was still on.

    You need the Pre Cat O2 sensor to be replaced.

    The light has not been since I changed it 1 month ago.

  6. #6
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Quote Originally Posted by nicksvana23 View Post
    Ok thanks. I just cleaned the MAF sensor and the light is still on. I'm changing the fuel filter now and if it's still running rough I'll check for a vacuum leak.
    The light may stay on until you've completed a certain amount of driving cycles. Best thing to do is clear the code by disconnecting the battery for 20 minutes and then see if it comes back. Better still, clear it with a code reader if you have one.
    goldse - I was about to say.... that looks like a big crack !
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    2003 fully loaded ZTW daily driver
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  7. #7
    Not Special Enough TXFO's Avatar
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Quote Originally Posted by Svt5.0 View Post
    vacuum leak
    this.

    SVTFs have problems with intake mani gaskets and the DSIM runners. try spraying carb cleaner around the mating surface and all the vac lines.
    TXFO V.2.0

    Hank Williams might have been a love sick drinker but being a love sick drunk don't make you Hank. -Sons of Bill-

  8. #8
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    well, I spoke too soon...my wife just called me and said that the CEL just came on again, and its the same code P0171. I have checked the PCV line, no cracks, replaced the PCV valve 2 months ago, looked at I think all the vacuum lines (I think) and cannot find the problem.

    Cleaned the MAF sensor one last time. Do you think it is the fuel injectors?

  9. #9
    goldsex's Avatar
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Causes for P0171

    • The MAF (Mass Air Flow) Sensor is dirty or faulty. There is an issue with some Vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
    • There could be a vacuum leak downstream of the MAF sensor.
    Resident AEM, K&N and Spectre Performance guy.

  10. #10
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Quote Originally Posted by goldsex View Post
    Causes for P0171

    • The MAF (Mass Air Flow) Sensor is dirty or faulty. There is an issue with some Vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
    • There could be a vacuum leak downstream of the MAF sensor.
    Do you have a diagram of the vacuum lines for 2002 ford focus?

  11. #11
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    I had the same problem for weeks, and my mileage dropped like mad. After lots of research I found this guide for the trouble code. I forget where I downloaded so I uploaded it to megaupload.

    ERROR CODE DIAGNOSTICS

    After all the trouble I found out that one of the vacuum hoses leading from the egr pipe to the dpfe sensor was collapsed. It was right near the end of the hose so I just cut it out and reattached. Mileage went right back to normal and my trouble code cleared.

    Hope this helps somebody lol.

  12. #12
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Quote Originally Posted by webmaster View Post
    I had the same problem for weeks, and my mileage dropped like mad. After lots of research I found this guide for the trouble code. I forget where I downloaded so I uploaded it to megaupload.

    ERROR CODE DIAGNOSTICS

    After all the trouble I found out that one of the vacuum hoses leading from the egr pipe to the dpfe sensor was collapsed. It was right near the end of the hose so I just cut it out and reattached. Mileage went right back to normal and my trouble code cleared.

    Hope this helps somebody lol.

    After looking over the Vacuum lines, I found that the line coming ou of the intake manifold and to the back of the PCV valve assembly was collapsed at the intake manifold. It was well hidden, and I did not find it the 4 other times I tried to fix this code, hopefully now it will clear.

  13. #13
    goldsex's Avatar
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    That is a common issue Here is a picture of it on my car....

    Resident AEM, K&N and Spectre Performance guy.

  14. #14
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Quote Originally Posted by goldsex View Post
    That is a common issue Here is a picture of it on my car....

    That is the same vacuum line yes, but since your line is collapsed, does it throw that code? OR do you think that there might be another leak, or possible another problem.

    My line looks exactly like that.

  15. #15
    goldsex's Avatar
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    Default Re: Engine code p0171 = System too Lean (Bank 1)

    Well it can cause a code Mine hasn't yet, it depends on how much it's collapsed. I would suggest you replace that tube. Contact Steve from Tulsey Ford he's a site sponsor and can get the parts shipped to you quickly and cheaper than you can get from your local delaer.

    I'm experiencing surging while I'm driving it's probably my DPFE sensor but the PCV hose can cause it too.
    Resident AEM, K&N and Spectre Performance guy.


 
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