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New to us Prius now has P0172

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by tony39rivera, Mar 2, 2023.

  1. tony39rivera

    tony39rivera New Member

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    Hello everyone. We purchased a 2007 Prius base last week with 135,000 miles with a warranties battery. Everything has been great over the first 350 miles until today. Yesterday, I put in new Denso spark plugs and new coils as I work to go through everything and tidy it up. It definitely ran smoother today. About 30 miles into the new plugs, I got the check engine light with P0172. Could the new plugs or coils cause this? I will get the MAF cleaner and try that, but I want to know if I should go back to old coils or plugs? Any thoughts are appreciated.
     
    #1 tony39rivera, Mar 2, 2023
  2. SFO

    SFO Senior Member

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    Welcome to PriusChat!!
    Unlikely that you would need new coils at 130k, unless the mileage isn't accurate (got carfax?).

    Did you purchase the plugs and coils at the dealer, local auto parts store, or someplace online?
    What make/model of plugs did you purchase?

    Here is the workup for DTC P0172 (and P0171) : 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

    FYI : you're moderated until you've posted 5 times.
     
    #2 SFO, Mar 3, 2023
    PriusCamper likes this.
  3. PriusCamper

    PriusCamper Senior Member

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    Great to see @SFO posting PDFs again! On first glance at the PDF my thought is that when you replace spark plugs on a Prius at the same time you need to clean the throttle body and use MAF cleaner on the MAF sensor then disconnect the battery to reset the system. As in you're only part way through the job and based on @SFO pdf I'm placing my bets on finishing the job...
     
    #3 PriusCamper, Mar 3, 2023
  4. tony39rivera

    tony39rivera New Member

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    Thank you very much for the information. The plugs were Denso SK16R11. I purchased them from Amazon. I also purchased the coils form Amazon. They were the best reviewed aftermarket ones. One of the original plugs I pulled out (leftmost cylinder) was slightly wet. For years, I have been in the habit of changing the coils with the plugs. I guess that wasn't needed this time. I can easily put the original coils back in. I also changed the air filter (which wasn't that bad) when I did the plugs. I will clean the MAF and throttle body (time to study how to do that on this car), and I will disconnect the battery. Hopefully that will get us running well. Other than that, it seems like a great car. Thanks again!
     
    #4 tony39rivera, Mar 3, 2023
  5. PriusCamper

    PriusCamper Senior Member

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    It's pretty easy... You can either stuff rags down throttle body and spray carburetor cleaner with some long tools to move the rags around, or you can buy an intake manifold gasket and pull the whole manifold to get it super clean...
     
    #5 PriusCamper, Mar 3, 2023
    mr_guy_mann likes this.
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    Maybe those parts you got from amazon are "legit" - or not. Counterfeit parts are a problem, esp on the web (ebay or amazon). Usually I would expect a bad ignition part to cause a misfire (or just not last as long as genuine Toyota or Denso - ie cause a misfire maybe 40-50k from now).

    Top of my list for P0172 is the MAF sensor- you have to remove it from the air filter housing to properly clean it.


    To really diagnose this I would use a scantool to monitor short and long term fuel trim while driving the car - fully warmed up at idle, moderate accel, and cruise. Seeing what trims are under different conditions can give a diagnostic direction.

    Fuel trim should ideally be 0% +/- 10%, if it goes below -20 to -25% or more, that's when it sets P0172.

    Look at this post. (In fact, it can be helpful to you to use the search feature to look through the Gen2 forums to see if others have had to deal similar problems)

    https://priuschat.com/index.php?posts/3319277

    Posted via the PriusChat mobile app.
     
    #6 mr_guy_mann, Mar 3, 2023
    Last edited: Mar 3, 2023
  7. tony39rivera

    tony39rivera New Member

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    2007 Prius
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    I
    Hello again. I have spent some time with the Prius trying to sort things out. I replaced the MAF with a new Denso one from the dealer just to make sure I had the best for that. With that l, I also cleaned the throttle body and unplugged the battery for a while. I also put the original plugs and coils back in. I also put in a bottle of BG 44k. Now, instead of the P0172, I am getting P0304. It seems to happen about once every 35-40 miles. It often seems to happen after I have driven for a while and then parked for a shopping trip. When I start going again, I will get some hesitation or skipping at idle when coming up to a stop sign. The car drives and accelerates normally other than this. And I get 43-48 mpg. Any new ideas?

    I am hoping to get a better scan tool to get some fuel numbers. I need to check through the forum to see what is recommended.

    If anyone knows a good shop for a Prius around Indianapolis, please let me know. Thanks for your help.
     
    #7 tony39rivera, Mar 12, 2023
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