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system too lean (bank 1)

Discussion in '1st Gen. Tacomas (1995-2004)' started by turnkey, Jan 25, 2010.

  1. Jan 25, 2010 at 12:36 PM
    #1
    turnkey

    turnkey [OP] New Member

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    I used a pocket scan code reader and got a PO171 system too lean reading. 2.7 liter 2001 eng. I don't know where too look from this point. Can anyone help?
     
  2. Jan 25, 2010 at 1:13 PM
    #2
    HondaGM

    HondaGM Roll Tide

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    check for air leaks from the throttle body to the air filter first
     
  3. Jan 25, 2010 at 4:15 PM
    #3
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Moderator

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    FlimFlubberJAM
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    MAF dirty, or a vacuum line leak
     
  4. Jan 25, 2010 at 4:24 PM
    #4
    shitroc

    shitroc Master of War

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    check your o2 sensors,bank 1 sensor 1 is your o2 sensor closest to the exhaust manifold,bank 1 sensor 2 is the the rear o2 sensor.You may just need to clean them or they may need replacing.
     
  5. Jan 25, 2010 at 4:25 PM
    #5
    shitroc

    shitroc Master of War

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    also check your mass air flow sensor,it might be just gummed up with oil and shit
     
  6. Jan 25, 2010 at 4:25 PM
    #6
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Moderator

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    Not for a "Too Lean" code. Start with the easiest things first. Vacuum leaks, Dirty MAF, THEN check the O2 and A/F sensors.
     
  7. Jan 25, 2010 at 4:36 PM
    #7
    shitroc

    shitroc Master of War

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    yah true enough
     
  8. Jan 25, 2010 at 6:25 PM
    #8
    derekp

    derekp giddy up!

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    I had a 2000 w/ the V-6 that threw the same code. I was told to change the downstream O2 sensor to fix it, so I did. $85 later, still there. Turns out it was the MAF that was AFU. Look the directions here: http://www.4runners.org/writeups/throttle/index.html and try the MAF cleaning. It is a helluva lot cheaper than the O2 replacement. IF that doesn't fix it, you aren't out too much...and you have a clean MAF sensor! (I didn't know about this site back then...I paid a guy to diagnosis and fix it...that hurt)
     
  9. Jan 25, 2010 at 6:35 PM
    #9
    macgyver

    macgyver Well-Known Member

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    My money is on a vacuum leak. My Honda Accord I had before the taco did the same thing. I drove around for six months on an expired tag trying to fix that damn code to pass emissions. After throwing many parts at it... Ended up being a vacuum leak.
     
  10. Jan 26, 2010 at 3:11 PM
    #10
    shitroc

    shitroc Master of War

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    mine started with that code so i first cleaned the maf sensor,didnt work,checked for leaks,same thing,replaced the maf sensor,still didnt work,replaced the o2 sensor and it cleared it. but now i need to replace the rear o2. lol
     
  11. Jan 26, 2010 at 3:25 PM
    #11
    derekp

    derekp giddy up!

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    Dude, that is Murphy's Law! If you would have started the other way it would have been your MAF or a simple vacuum leak...
     
  12. Jan 26, 2010 at 3:27 PM
    #12
    tc2008

    tc2008 Well-Known Member

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    I got that same reading when my exhaust was leaking...
     
  13. Jan 26, 2010 at 3:40 PM
    #13
    kws129

    kws129 Well-Known Member

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    Be cautious on the O2 sensors, on most of the 2.7L bank 1 sensor 1 (nearest the exhaust manifold) is actually an air fuel ratio sensor. That went bad on my old taco and I got a no signal bank 1 sensor one code. I had a more advanced scan tool and I could look at the signal from that sensor to see if anyone was home.

    If you are in doubt I would consult someone with a more advanced scan tool as I recall this senso being quite expensive ($150 +)
     
  14. Jan 26, 2010 at 3:55 PM
    #14
    turnkey

    turnkey [OP] New Member

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    Thank you for all the suggestions. So far I've cleaned the MAF, changed the spark plugs (NGK bkr5eix 6341), cleaned the throttle body, and I am going change the fuel filter. I bought the O2 sensors but I'm waiting until I've tested everything out before I put those in. I'll give you the update soon.
     
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