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P0401

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Swayde96, Jul 16, 2021.

  1. Swayde96

    Swayde96 Junior Member

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    I have been battling this code for a while now on my 2010. I cleaned the entire EGR system and replaced every gasket. Those didn’t work so I replaced the EGR valve, code went away after that for about two weeks (700 miles) and then just came back. What are all the potential causes?


    iPhone ?
     
    #1 Swayde96, Jul 16, 2021
  2. wheezyglider

    wheezyglider Active Member

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    Here's what the repair manual shows as potential causes.

    upload_2021-7-16_10-31-36.png

    It's pretty much what you just worked on. Sometimes people don't realize they need to clean the EGR cooler and they stop at the EGR valve and the EGR pipe. Sometimes people clean the intake manifold but miss the tiny EGR openings that feed each cylinder. You pretty sure you got those?
     
    #2 wheezyglider, Jul 16, 2021
  3. ChapmanF

    ChapmanF Senior Member

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    Here's another thread where a mystifying P0401 finally got tracked down.

    In that case, it was a problem in the valve, which I think you have eliminated by replacing the valve. So I don't suggest that you will find the same ultimate cause as in that other thread, but you might find some use in the techniques used to chase it down.
     
    #3 ChapmanF, Jul 16, 2021
  4. PriusCamper

    PriusCamper Senior Member

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    Did you do much cleaning when you replaced your EGR? Seems like you didn't do enough cleaning?
     
    #4 PriusCamper, Jul 16, 2021
  5. amarino

    amarino Member

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    When you replaced the EGR valve was it a newer part revision / kit? Or where did you get the "new" valve from? I believe there was a newer part and it also needed a software update to go with it. This video mentions that as well.
     
    #5 amarino, Jul 16, 2021
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