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Cant fix P0171 (System Too Lean Bank 1), I got data freeze

Discussion in '1st Gen. Tacomas (1995-2004)' started by cezzz, Jun 9, 2020.

  1. Jun 9, 2020 at 8:47 AM
    #1
    cezzz

    cezzz [OP] New Member

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    So I got the tricky code P0171 and have been cleaning a replacing parts over time but it is now time to go Smog my truck and get it fixed without paying an arm and a leg, I was hoping to get some input. The light tends to be activated when i am on the freeway so above 50mph based on the data freeze.


    Its a 2002 Tacoma Pre-runner V6 2WD, just short 200,000 miles

    Cleaned the MAF
    Cleaned Airfilter (K&N Cleanable filter).

    Replaced the following:
    O2 sensor in bank 1(One closest to the engine, between the engine and catalytic converter) with Denso 234-9001 Air Fuel Ration Sensor
    Fuel Filter

    Checked the hoses for any leaks and nothing i could visually see, sprayed water on the hoses to get a better visual idea.

    A few months ago also got code P0120 - Throttle/pedal Position Sensor/ Switch A Circuit
    Resulted in replacing Throttle Position Sensor with a new OEM one and code has not come back.

    I was hoping someone can help me decode the data freeze, I can def see the fuel trim is jumping quit a bit, but cant decode it. I tried looking for similar situations on the forums.

    Data Freeze:
    Short Term Fuel Trim - Bank 1 : 3.1%
    Long Term Fuel Trim - Bank 1 : 39.1%
    Engine RPM: 2029 rpm
    Vehicle Speed: 58 mph
    Calculated LOAD Value : 46.3%
    Engine Coolant Temp : 147.2 degrees F
    Fuel System 1 Status : CL
    Fuel System 2 Status : N/A


    Idle reading:
    Short Term Fuel Trim - Bank 1 : 2.3%
    Long Term Fuel Trim - Bank 1 : 14.1%
    Engine RPM: 973 rpm
    Vehicle Speed: 0 mph
    Calculated LOAD Value : 18.8%
    Engine Coolant Temp : 125 degrees F
    Fuel System 1 Status : CL
    Fuel System 2 Status : N/A
     
  2. Jun 9, 2020 at 9:44 AM
    #2
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Stock. EZ pass.Dump pass.Inspection sticker.Convict printed lic.plates.FG cap.
    Welcome aboard new member
    Best way to check for vac hose leaks is carb cleaner or propane sprayed on hoses while engine idles.
    Exhaust leaks before B1S1 A/F sensor can trip code also.
    Worse case scenario
    Low fuel pressure from fuel filter
    Even worse failing fuel pump
    Have fuel pressure tested
    @cezzz
     
    Last edited: Jun 9, 2020
  3. Jun 9, 2020 at 9:59 AM
    #3
    Black DOG Lila

    Black DOG Lila Well-Known Member

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  4. Jun 9, 2020 at 10:30 AM
    #4
    tony2018

    tony2018 Well-Known Member

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    Could also be an exhaust leak.
     
  5. Jun 9, 2020 at 11:38 AM
    #5
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Or injectors
     
  6. Jun 9, 2020 at 9:40 PM
    #6
    Glamisman

    Glamisman Well-Known Member

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    2 things right away... your engine coolant temp is way too low and the second is your PCM is trying to add 39% MORE fuel according to what the front O2 sensor is reading. Your sensor 234-9001 is for an automatic trans, the 234-9003 is for a manual trans... maybe the wrong O2 sensor? Another possibility is check the air boot between the throttle body and the MAF... Take it off all the way and twist it, flex it etc, you are looking for cracks in the expansion/contraction bellows and any splits where it seals.
     
    cezzz [OP] and nagorb like this.
  7. Jun 9, 2020 at 9:56 PM
    #7
    Rastopher

    Rastopher Member

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    Portland, Oregon
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    2002 2.7 4x4 reg cab automatic
    Utility Shell, Alloys, poly steering rack bushings, aftermarket audio system.
    I just had this, went down every single road here. My oem MAF was lazy, failing in spec. Even after cleaning it would respond to change but wasnt reporting all the airflow accurately. This effectively meant that unmetered air was getting in, just like a vacuum leak. Bought a delphi maf for 80 bucks off their Amazon store and it was an immediate fix. I’m writing a full writeup soon but if you have specific questions pm me.
     
    Akkording, cezzz [OP] and cruiserguy like this.
  8. Jun 9, 2020 at 10:16 PM
    #8
    nagorb

    nagorb Should be a dang perma mod

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    Long term fuel trims are waaaay high. Could be a sensor, but could be a vacuum leak, I've had leaks that didn't show with the water/carb cleaner/whatever, needed a smoke machine to find it. I would clean the maf, throttle body, iac valve.

    Also is the k&n one of the type that you oil? That there could be the problem.
     
    cezzz [OP] likes this.
  9. Jun 30, 2020 at 2:30 PM
    #9
    cezzz

    cezzz [OP] New Member

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    It was the MAF sensor, I cleaned it multiple times but i guess it wasn't doing anything since it was faulty/broken. Replaced it and check engine didn't turn back on, Drive 200+ miles and drive cycle, smog passed and good to go.

    Bought the Denso 197-6020 Mass Air Flow Sensor from Amazon for $73
     
  10. Jul 2, 2020 at 10:45 AM
    #10
    nagorb

    nagorb Should be a dang perma mod

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    Awesome! Glad you figured it out.
     
    cruiserguy likes this.

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