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Vehicle P0171

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by sunnykoomos, Aug 16, 2021.

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  1. sunnykoomos

    sunnykoomos New Member

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    2006 Prius
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    I have a Prius 2006 with 98,000km

    Sat, Engine lights on, ODB report P0171, Long term Fuel Trim is 29%, still drive well
    Sunday, tried some DIY fix and clear the code, engine runs worse than before
    Monday, Engine light pop up again after 5 mins drive, LTFT 41% after 45 mins of driving

    Symptoms:
    STFT high in low rpm, back to normal in 2000+rpm
    Short term Fuel Trim stuck at 0% after I unplug the MAF, LTFT 39%

    Suspect issue:
    1. MAF
    2. O2 sensor
    3. Fuel injector (I did use fuel addictive though)
    4. Fuel pump (Filter changed this year)
    5. Leaking

    Googled for 5+ hours still no clue so I would like some help. Thank you

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG] \

    More data:
    photos.app.
    goo.gl/
    Re1LteWWgz7yHk7p9

    ^Newcommers can't post link :(
     
    #1 sunnykoomos, Aug 16, 2021
  2. SFO

    SFO Senior Member

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    #2 SFO, Aug 23, 2021
    Raytheeagle likes this.
  3. sunnykoomos

    sunnykoomos New Member

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    Thank you for the doc.

    I found out it was a vacuum leak, after replacing new seals and O-Ring.
    Short term fuel trim is stable now but the long term still stick to positive 30%+.
    ( Edit: I clean the MAF sensor already)
    [​IMG]

    I tried disconnect the MAF, it runs smoother without knok/misfire, but LTFT still 30%+
    [​IMG]

    Any suggestion?:(
     
    #3 sunnykoomos, Aug 24, 2021
  4. SFO

    SFO Senior Member

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    Which seals and O-ring did you replace?

    What did you use to clean up the MAF sensor?

    What obd2 codes (DTCs) are you retrieving now?
    Since you cleaned the MAF, now reset the learned mapping by disconnecting the 12v source for a period of time.
     
    #4 SFO, Aug 24, 2021
  5. sunnykoomos

    sunnykoomos New Member

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    I replace the injector seals and O-ring.
    [​IMG]

    What did you use to clean up the MAF sensor?
    I use Carb cleaner to clean the MAF as I can't find any MAF cleaner around me.
    Spray 3-times and let it dry, then reinstall.

    What obd2 codes (DTCs) are you retrieving now?
    I got P0171 system too lean just like before, but the fuel trim behave differently.

    [​IMG]
    [​IMG]

    Is MAF staying as 1.9-2g/sec idle a bit low? I saw Youtube videos says it should be around 3.
     
    #5 sunnykoomos, Aug 24, 2021
    SFO likes this.
  6. SFO

    SFO Senior Member

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    Did you have a chance to disconnect the 12v source, which will reset the ECUs ??

    Have you already worked step-by-step through the above posted diagnostic for DTC P0171 ?? (including steps #4, #10, #11, #12)

    https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2054m/cip0171.pdf

    Which OBD2 scanner are you currently using, as you may need to use 'techstream' to continue with your diagnostics.
     
    #6 SFO, Aug 24, 2021
  7. TMR-JWAP

    TMR-JWAP Senior Member

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    When you cleaned the MAF, did you clean one or both of these? The top photo is the MAF sensor element. The bottom photo is the temperature sensor bulb. I learned my lesson the hard way.

    MAF Sensor.jpg Temperature Bulb.jpg
     
    #7 TMR-JWAP, Aug 24, 2021
  8. sunnykoomos

    sunnykoomos New Member

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    Sorry for busying last week.
    I tried disconnect the 12v battery yesterday, DTC P0171 code pop up today again.
    Fuel trim behave same as before. LTFT at 30%

    Just tried doing step 4c, THA(4)-E2(5) showing 10.7k ohms at 27*C room temp.
    Seems to indicate a bad MAF :(

    I also tried asking my known mechanic for a fuel pressure gauge, unfortunately he doesn't has one :/
     
    #8 sunnykoomos, Aug 29, 2021
  9. sunnykoomos

    sunnykoomos New Member

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    Haha I did the same thing before, I found that in Google after I bought the carb cleaner

    This is what looks like now after cleaning
    [​IMG]
     
    #9 sunnykoomos, Aug 29, 2021
  10. sunnykoomos

    sunnykoomos New Member

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    Correction*
    THA(4)-E2(5) showing 1.8k ohms at 27*C room temp.

    Docs says it should be
    2.21-2.69k ohms at 20*C
    0.49-0.67k ohms at 60*C

    Mine seems a bit off
     
    #10 sunnykoomos, Aug 29, 2021
  11. TMR-JWAP

    TMR-JWAP Senior Member

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    I also found that just spraying the MAF cleaner down in the hole to flush the sensor wasn't enough. I continued to get the P0171 afterward, until I gently cleaned it with a Q-tip that had been wetted with MAF cleaner immediately after spraying it.
     
    #11 TMR-JWAP, Aug 29, 2021
  12. ChapmanF

    ChapmanF Senior Member

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    Looks about spot-on to me. Note the y-axis is log-scaled.

    tha.png

    This test is only of the intake-air temperature sensor (the bulb on the side of the MAF sensor). Is that what you're interested in testing?
     
    #12 ChapmanF, Aug 29, 2021
  13. sunnykoomos

    sunnykoomos New Member

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    I decide to spray it 5 more times and use a Q-tip, no changes to LTFT.

    I was wondering, if the LTFT stuck at 29-35% no matter MAF is connected or not, does this indicate the MAF is not the problem?
    (Since the ECU will use the default table, which should improve LTFT if bad MAF is the problem?)
     
    #13 sunnykoomos, Aug 31, 2021
  14. ChapmanF

    ChapmanF Senior Member

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    Following the diagnostic instructions that SFO provided in post #2, have you measured the fuel injection volume and found a proper value (36 to 46 ml per 15 seconds) as in step 3? Have you measured the fuel pump pressure and found a proper value (304 to 343 kPa) as in step 7?
     
    #14 ChapmanF, Aug 31, 2021
  15. Prius RT

    Prius RT Junior Member

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    Where is this temperature sensor bulb? Why has that to do anything with p0171?
    I cleaned the MAF and replaced air filter. I am getting p0171 now. 3x in last 75 miles
     
    #15 Prius RT, Aug 4, 2023
  16. SFO

    SFO Senior Member

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    All part of the same piece of plastic, inspect carefully.
    Should I post the 'factory workup' for DTC P0171, or can you find it?
     
    #16 SFO, Aug 5, 2023
  17. dolj

    dolj Senior Member

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    In post #7 above, the first image is the MAF sensor wire that needs cleaning. The second image show the temperature sensor. This also may need cleaning.
     
    #17 dolj, Aug 5, 2023
  18. Prius RT

    Prius RT Junior Member

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    Thanks. Cleaned MAF sensor second time esp MAF wire that's inside and the amber bulb. Reset code by unplugging battery. Will drive and see if p0171 comes back

    This is how I am proceeding chronologically:

    Replaced Air filter
    Clean MAF sensor
    Replace MAF sensor
    Check for vacuum leak
    Fuel injection cleaner
    Replace upstream O2 sensor
    Replace fuel filter
    Replace fuel pump
     
    #18 Prius RT, Aug 5, 2023
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