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P0171

Discussion in 'Gen 2 Prius Technical Discussion' started by Cometflash, Jun 5, 2021.

  1. Cometflash

    Cometflash Junior Member

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    I have tried the cleaning of MAF sensor so far.

    The code pops up every time I do a curve (during acceleration), or I gas in a slight elevation.
    If I gas easy or pushing acceleration the code does not come out, even at high speeds.
    No mpg difference that I have noticed.

    I have ob2 reader, and an app that gives the option in the video below. Not sure which readings would be something to look at to help diagnose.

    I try getting diagnosed at Toyota once, they told me was the 12v battery, but I had that put up just 3 months ago, and had warranty on it. Showed Toyota findings and got a new battery on. Purchase a battery charger to charge this battery full.
    Charged full to 13.7, and idle after 24 hours on staying at 12.5, but with all lights on, and no 0 ready on, it stays at just 12v, not sure if this is acceptable for a new battery.
    With everything on is high on the 14v range.

    I just hope is not a fuel pump, have being putting lots of time fixing some other things. Got both battery in, fixed the odometer meter screen, and got a new inverter pump installed, all of which satisfied all the other codes I had, but this one is just too many possibilities.
    A question I have also, is if you guys feel is Ok to try a injector cleaner, in case such could be a problem, and if there is any chance to solve the issue in case it is due to injectors.

    Doing a few drives around I can see oxygen readings and the MAF readings, so I know they at least not dead, but know they still could be at fault.



     
  2. PriusCamper

    PriusCamper Senior Member

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    If I were you I'd buy a used MAF sensor from a local wrecker, or online and see if that addresses the problem. It's such an old Prius it'd probably not be worth it to listen to Toyota and replace with brand new over-priced parts.

    Also, what's the app you're using to get all the information from your Prius? It doesn't seem like an app I'm familiar with and that could also be the source of the problem, as some apps & code readers are not reliable as others.
     
  3. Cometflash

    Cometflash Junior Member

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    I got the ob2 reader recommended by doctor Prius, but got this app as well because it gives more in debt information.
    I'm actually thinking it could be the O2 sensor now, after watching some videos, because the voltage on the 02 at times gets very low. But I try checking them last night, and even though I noticed this the code never showed up on the travel I did last night.

    The app in the video is simple called carscanner.
    Drprius finds the exactly same code.

    On the carscanner app I can plug in my exact car model and such, and it only scans for things the app is comparable with my car.
    That is a very large list of things this app scan for, but many are things newer cars have.
     
  4. Cometflash

    Cometflash Junior Member

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    I also saw that the MAF readings should pair throttle readings well, and they match quite close when I run the car and compare the two side by side.

    Oh, I forgot to mention: this is for a Prius 2004.
    Miles read 175k, but keep in mind I had the dashboard out for some time, so the milage would be a bit higher.
    When I changed the pump, I also noticed that it wasn't the original one, so Toyota likely exchange on the recall, with previews owner.
    I have the car for about 5 years now. Only now started getting problems, which started after I visit the scorching Texas.
    I'm in Colorado now.
     
    #4 Cometflash, Jun 6, 2021
    Last edited: Jun 6, 2021
  5. TMR-JWAP

    TMR-JWAP Senior Member

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    A good thread to read...and a lesson I learned on the P0171 on a Gen 2. The MAF sensor assembly must be removed from the throttle body to properly access and clean the elements.

    P0171 System Too Lean (Bank 1) | PriusChat
     
  6. Cometflash

    Cometflash Junior Member

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    I did took the MAF sensor, and used the MAF sensor cleaner and let it dry for about 12 hours before I put back in.
    Took for a drive, and right away the code came back on the drive off.
    The sensor look pretty clean as I took it out, but I spray it good anyways, letting drip in a vertical way as I seen some videos suggesting.

    Edit: also I try that over a month ago already, and code persists
     
    #6 Cometflash, Jun 6, 2021
    Last edited: Jun 6, 2021
  7. TMR-JWAP

    TMR-JWAP Senior Member

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    The temperature bulb is the only part that's visible until after you remove the sensor. You also cleaned the 2 sensor elements that are down inside, not just the amber bulb that's out in the open? You would also probably be surprised by how much gunk comes off the elements if you soak a Q-tip with the cleaner and use it to gently wipe the elements. Spray alone doesn't do a very good job.
     
  8. mr_guy_mann

    mr_guy_mann Senior Member

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    Did you carefully clean the two sensing elements visible from the "end" of the MAF? 20160919_104130.jpeg

    Posted via the PriusChat mobile app.
     
  9. Cometflash

    Cometflash Junior Member

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    Took everything apart, clean again sensor, cleaned throttle completely. Throttle was pretty dirty.
    My gas mileage went down, acceleration got much better. Ran for a while yesterday, no codes.

    Today around the mall area, taking a curve, code came back again on engine light, so, at least cleaning can't be a problem.
    The MAF actually look good. But did a cleaning all around again just in case.
     
  10. edthefox5

    edthefox5 Senior Member

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    Faulty or dirty fuel injector.
     
  11. mr_guy_mann

    mr_guy_mann Senior Member

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    I don't know your skill levels or what tools you have. Things that could cause a P0171: bad MAF or wiring, air induction leak downstream of the MAF (such as PCV hose, purge valve or hose, intake manifold gasket, lower injector o-ring, etc), restricted fuel injectors, low fuel pressure, too much ethanol (E85) in the fuel tank, faulty A/F sensor, or exhaust leak near the A/F.

    You can do as others here have done- start throwing parts at the problem and pray it fixes it. If you use cheap parts you could be installing a different problem as well.

    Another path is to get a copy of the factory srrvice manual and educate yourself about how the system works and what the ecu sees when it sets the code. Then start testing as the manual dictates.

    Useful scan data would be to see the MAF airflow rate, A/F sensor and O2 sensor voltage, Short and Long Term Fuel Trims- all with engine fully warmed up; at idle, light accel, steady cruise and when the fault occurs. Have a scantool that can record or log data makes this much easier. Also posting the freezeframe data for the fault code can help.

    Posted via the PriusChat mobile app.
     
    BDenis likes this.
  12. PriusCamper

    PriusCamper Senior Member

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    Yes, what this person says here... Also my latest hunch as a contributing factor is a tank of bad gas...
     
  13. Cometflash

    Cometflash Junior Member

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    Thanks for letting me know the types of scan data I should look for.
    I'll do some test drives with those readings running on the background and post as soon as I get them.

    I did one before cleaning the throttle running the throttle and MAF sensor on the background
    I notice the code came out just as it hit 36% on the throttle reading.

    I didn't get the time to do a drive with readings on the background after cleaning, but I'll try to do so ASAP, and test the other things you mentioned as well.
    Only problem with app that I have is that I can only test 2 things at the time, unless I purchase the app.
     
  14. Cometflash

    Cometflash Junior Member

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    The test before cleaning the throttle a and MAF sensor.

     
  15. Cometflash

    Cometflash Junior Member

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    Test done driving the car and stopping once check engine pop up.

    The test below was done after I let the gas tank run close to empty, put engine cleaner on tank, filled up with the highest octane available on a chevron gas station, and use the tank to about half before performing test.

    When I left the gas station with full tank the check engine light came out just as I left the gas station on the turn to the road.
    The highest mph I have seen the code was around 42mph.
    Usually happens in the high 30s, but my last test, which was the fuel trim high/low, the code popped up going only at 17mph.

    After I post this I'll try to upload screenshots.







     
  16. PriusCamper

    PriusCamper Senior Member

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    What app are you using for all these screenshots?

    At this point I'm thinking swapping your MAF sensor with a friend would be worth a try...

    And perhaps something in the wiring that's affected only by a turn under hard acceleration?
     
  17. mr_guy_mann

    mr_guy_mann Senior Member

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    You need better tooling- IDK if something like Torque can graph more data at once, but being able to view all the data that I mentioned before at one time really helps in figuring out what is going on. In your video capture of A/F and O2 sensor data, I really don't like the A/F from about 1:30 to 2:30 in the video. The A/F goes up to 5V and then slowly drops to 4V (extremely lean). The A/F should only reach 5V during fuel cut decel or engine shut off- but at that time the downstream O2 is reading 0.9V- very rich.
    Even when the A/F was showing kind of normal (around 3.3V), the O2 was still mostly at 0.9V (normal is usually around 0.7V)

    You might have a faulty upstream A/F sensor, but I need to see ALL the data in one capture to give a better opinion.
     
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  18. Cometflash

    Cometflash Junior Member

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    I could buy the pro version.
    The pro version of the one I have is 3 dollars, torque looks to be about 5 dollars, but if you know torque, have used and recommend it, I rather get something more familiar to you.
    Would buying torque pro allow me to provide the information to you?
     
  19. mr_guy_mann

    mr_guy_mann Senior Member

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    My reccomendation would be to get a mini VCI cable from amazon or ebay along with a bootleg copy of Techstream and install it on an old windows laptop. That would give you the diagnostic software that the dealer uses- you can get codes and data from all the modules on the car, record "movies" of all that available data, and perform tests and procedures that are only possible with a FULLY capable scantool. But it can be fiddley to install and is $30-40 plus a laptop.

    I mentioned Torque app only because it's popular and I know it can display multiple data at once- do not know how it is for recording data. When I am doing diagnostic work, I use a "full" scanner like Techstream, Snapon, or Autel. Haven't tried doing much with an app.

    Posted via the PriusChat mobile app.