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P0171 headache. Help!

Discussion in 'Generation 1 Prius Discussion' started by Malson44, Oct 14, 2019.

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  1. Malson44

    Malson44 New Member

    Joined:
    Oct 9, 2019
    1
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    Location:
    Pennsylvania
    Vehicle:
    2002 Prius
    Model:
    N/A
    My troubles started in January 2019 with my Gen1 Prius. Spark plugs (4) and coils (4) were changed due to a misfire. In April the vehicle threw a code for engine misfires again but this time the PCV was changed, and throttle body was cleaned as well. Drove well for a few months, then I threw an other misfire code so fuel injectors, coils, and spark plugs were all changed. The misfire was so bad in August Before the parts change that I thought I blew a rod, it was hitting so hard I thought the motor was done. September Mass flow sensor was changed and O2 sensor was changed for P0171. I’m still getting a P0171 and I’m ready to call it quits. Even though I love my 2002 Prius. No misfire codes after coils, plugs, and injector change in August just P0171.

    *note* after the fuel plugs were replaced I went from 39 miles to the gallon to almost 50 miles per gallon. I’m still getting really good gas mileage but P0171 is showing (running lean). The vehicle only throws the code under 30mph. The car is driven 90 percent highway. It also feels as if it throws this code coming to a coast and the electric motor takes over or the gas motor turns on. I’m ready to toss the towel in. Please help keep this Prius 1 alive.

    January 2019- Spark plugs and coils changed.

    April 2019- Throttle body cleaned and PCV changed.

    August 2019- Fuel injectors replaced
    August 2019- spark plugs coils changed

    September 2019- Mass flow sensor changed
    September 2019- O2 sensor changed
     
    #1 Malson44, Oct 14, 2019
  2. gothstone

    gothstone Junior Member

    Joined:
    Sep 29, 2019
    36
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    Location:
    KC MO
    Vehicle:
    2002 Prius
    Model:
    N/A
    Sounds like vacuum leak to me, probably just a rotten hose. I would just rip off each vacuum hose (1 by 1 if your not sure you can keep track of it all) run to an auto parts store and get appropriate sizes and lengths cut. Will only cost a few bucks. I always find just replacing old vacuum lines to be faster and more productive than trying to find the leak. Can't get to the manuals right now, but IIRC the prius vacuum system is pretty short and simple.
     
    #2 gothstone, Oct 14, 2019
  3. Q*bertZ

    Q*bertZ Member

    Joined:
    Oct 22, 2019
    155
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    Location:
    greenville south Carolina
    Vehicle:
    2002 Prius
    Model:
    N/A
    I also get a P0171 at about 35 mph. But I'm not getting 50 mpg. I don't think that error code is going keep your car from running. Mine has been running fine for years with that code.
     
    #3 Q*bertZ, Nov 11, 2019
  4. Josey

    Josey Active Member

    Joined:
    Jun 10, 2019
    287
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    Location:
    Virginia
    Vehicle:
    2003 Prius
    Model:
    One
    Can you clarify this? "it was hitting so hard I thought the motor was done." There's this thing called engine "knock" or "ping" - sounds like someone maybe shaking a can of marbles under the hood. It can occur with an actual lean condition. (O2 sensor replacement is a common response to a P0171, but that's sometimes shooting the messenger).

    Do you have any manner of scantool? Even a simple, generic one that will record live data? Basic ones can be had for cheap. You'd want to drive around and record some data and look at the "fuel trims".

    Otherwise, what gothstone said - vacuum leaks. The hoses are one spot, but it can be any air leak downsteam from the MAF. Intake manifold gasket. Throttle body gasket. Stuff like that.
     
    #4 Josey, Nov 11, 2019
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