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P0171 every 5 months

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by 05_silver, Aug 31, 2023.

  1. 05_silver

    05_silver Junior Member

    Joined:
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    Vehicle:
    2005 Prius
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    N/A
    I cleaned the MAF sensor in accordance with the instructions here. The code then goes away for about 5 months. It goes away long enough for me to believe that the MAF sensor is at fault or needs cleaning but I am not entirely sure.

    I have even replaced the MAF sensor.

    I would like to know what this is without going down too many difficult rabbit holes if at all possible.

    One thought is that I am using a cheap air filter that is non-Toyota and I live off of a dirt road. Maybe the filter allows more in than the OEM? 95% of my driving is not on this dirt road so I am not 100% sure about that.

    Any ideas?

    Thanks.
     
    #1 05_silver, Aug 31, 2023
  2. JC91006

    JC91006 Senior Member

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    Try cleaning the throttle body
     
    #2 JC91006, Aug 31, 2023
    05_silver likes this.
  3. mr_guy_mann

    mr_guy_mann Senior Member

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    Vehicle:
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    What scantool are you using? What brand of MAF sensor did you install?

    Here's a list of "known good" MAF readings for my 2006 under different operating conditions. How does your car compare?

    What are Short Term and Long Term Fuel Trim values? - at "hot idle" - (1000RPM), at 2000RPM, at steady 45mph cruise, and at faster speeds.

    What does the upstream Air/Fuel sensor voltage show at same conditions? Screenshot_20220825-002058.jpeg

    Posted via the PriusChat mobile app.
     
    #3 mr_guy_mann, Sep 1, 2023
  4. 05_silver

    05_silver Junior Member

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    Wow, never saw this. I will go ahead and clean the TB then. I replaced it with an OEM MAF (Denso) I believe. Putting back the old MAF results in the same scenario so I know it is not that. I do not have a scan tool for this purpose. Honestly with 5 other different branded vehicles the need to buy new scan tools does add up. I appreciate the info and when I am positioned to purchase a scan tool or perhaps use existing hardware or software laying around I will check into it further since the freaking light just popped up again.

    Thanks!
     
    #4 05_silver, May 5, 2024
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    Some ECM (engine) data is covered by generic OBD2 protocols. Stuff like RPM, MAF, ECT, fuel trims, etc are pretty much "the same" for most any 1996 & newer car sold in the US.

    So if you already have some type of scantool, it should have OBD2 capability and be able to give you some engine data.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, May 6, 2024
    Leadfoot J. McCoalroller likes this.
  6. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Agreed. It's very likely that one of the tools you already own can read the basics out of a Toyota, and fortunately you only need basic fuel injection info to solve this one.

    You probably don't need to spend money until this car shows a hybrid-related code
     
    #6 Leadfoot J. McCoalroller, May 6, 2024
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