P0171 code help needed

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Razim, Dec 13, 2024.

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  1. Razim

    Razim New Member

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    I need any advice anyone can give me. I have a 2013 Prius Two that I bought new. Currently 155,000 mi and now having a P0171 code occurring. Car is running okay, no misfires, don’t use oil, the only thing maybe is a drop in highway mpg’s 45 was 48.
    List of things I checked or replaced.
    1 Replaced both ventilation hoses plus PCV.
    2 Replaced 3 fuel vapor hoses in engine compartment and checked the valve for closure when not energized.
    3 Replaced the intake manifold and associated gaskets.
    4 EGR system, replaced all gaskets and cleaned valve, cooler & pipe.
    5 Replaced intake air flow meter sensor (MAF).
    6 Replaced Fuel Gas Cap, Spark Plugs, and (Engine Air Filter,Not a OEM item).
    7 Checked Fuel pump pressure and bleed down times, Pump on 49 psi, Pump off 5min-40psi, 10min-37psi, 15min-33psi, 20min-31psi, 25min-29psi and 30min-26psi.
    10 Checked upstream A/F sensor with my scan tool and seems to respond okay, but I am not absolutely sure.
    I sprayed the new intake manifold with ether and had no change in engine rpm’s.
    Also, did a smoke test and found no leaks in new intake manifold or engine.
     
    #1 Razim, Dec 13, 2024
  2. Tombukt2

    Tombukt2 Senior Member

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    Wow. You really want this car to be a keeper for you hey wow I don't know buddy It doesn't look good for the home team but yeah this is not the one you want to be trying to do all this to but you're deep in it.
     
    #2 Tombukt2, Dec 14, 2024
  3. Brian1954

    Brian1954 Senior Member

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    That is an impressive list of things that you already checked. I do not think that I can be of much help. I do have one question. What is the long-term fuel trim?
     
    #3 Brian1954, Dec 14, 2024
  4. Razim

    Razim New Member

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    Freeze Frame had it at 29.688%. Short was 5.469%. I’m only guessing now, the fuel pump seems to functioning properly and doesn’t look if I have leaky injectors or fuel pump. For all I know it could be a bad A/F sensor.
     
    #4 Razim, Dec 14, 2024
  5. Razim

    Razim New Member

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    Yes, I do want to keep it. This the first time I had any trouble with it. I usually can figure things out but this one’s little difficult.
     
    #5 Razim, Dec 14, 2024
  6. Tombukt2

    Tombukt2 Senior Member

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    Yes Sir good luck.
     
    #6 Tombukt2, Dec 15, 2024
  7. Eddie25

    Eddie25 Active Member

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    Try to see what happens to the fuel trims in various driving situations. A graph with long term and short term fuel trims plus engine RPM might prove helpful to narrow it down a bit.

    If I remember correctly, you can do a throttle blip and watch the A/F sensor reaction to verify functionality. Maybe you could post a picture of that graph and compare it with someone on the forum.

    What MAF sensor did you get? That's a part you only want to get OEM/Denso from a trusted source. If you got either aftermarket or even OEM/Denso from ebay or something, then I would still not consider it to be ruled out. You could try cleaning the old one and see what happens.

    I assume you did a visual check on the throttle body at some point.

    If all that stuff checked out and the data doesn't lead you a different way, I think I'd try fuel injector cleaner or inspection.
     
    #7 Eddie25, Dec 15, 2024
  8. Razim

    Razim New Member

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    Two
    The scan tool that I have, does have a A/F sensor check. The values looks okay based on what I know and what I read about them. I am not an expert on them. I will post the values and graph later.

    The MAF sensor did come from Toyota dealership.

    When I worked on the Intake, I did check the throttle body and I was surprised it wasn’t that oily on the bottom. Everything was cleaned up then before reinstalling. The gasket was also replaced and the throttle body bolts retorqued.

    I have been putting injector cleaner for little while now already.
    The car drive with no hesitation and great acceleration. Lower mpg’s and a check engine light is the only thing.
    I do appreciate all the help that you’re giving me.
    Thank you
     
    #8 Razim, Dec 15, 2024
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