Interesting P0401 Code

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by 2011Prii, Aug 20, 2019.

  1. 2011Prii

    2011Prii Junior Member

    Aug 20, 2019
    2011 Prius
    Hi all,

    Sorry, but this may be long winded...
    I am a relatively new owner of a 2011 Prius. I bought it with 179k miles a few months ago with a suspected bad head gasket (knocking on startup with intermittent cylinder 3 misfire).

    I trailered the car home, immediately cleaned the egr cooler, egr valve, egr pipe, intake manifold, and map sensor. Also replaced plugs, swapped coils, new pcv valve (and added a catch can), did an oil change, coolant flush, and transmission drain and fill. I drove the car for a bit and started getting the P0401 code. I also noticed cylinder 3 seemed wet (confirmed with boroscope).

    I decided to pull the head and replace the head gasket (spent maybe 12 hours doing that...THANK YOU to those of you that have given direction on the job). My problem was the black "sealant" on the head gasket wore away between a coolant passage and cylinder 3, so fluid was leaking in there very slowly. I also decided to removal ALL egr components again to give them a more thorough cleaning. They are now nearly spotless...even the small holes in each intake port and especially the cooler.

    Well, the car idles, runs, and drives fine. I've been getting 60mpg this whole time (I'm a mild hypermiler). I downloaded techstream and just today did the egr step test and confirmed my egr valve is opening and closing like it should. (No, there's no sticking with it whatsoever). I'm just at a loss of what to do next. I tested the vacuum switch with 12 volts and confirmed that it is operating. I checked for vacuum leaks to no avail. I have taken things off and checked and double checked and am not sure what to try next. The MAP sensor shows changes as I drive, but I'm not sure what the values should be. Maybe there's a possibility it's working, but not within the range that it should? Any insight on this at all? I just want to get this behind me so I don't have to worry about doing all the work I've done over again.

    I should also note the egr valve magnet does not appear to be getting stuck in the fully closed position. I thought that may be my problem at one point after reading another member with that problem.

    Thank you in advance and thank you to those that contribute to this forum. It's been very helpful in my short time of ownership. Also, I apologize if this was started in the wrong sub-forum.
    #1 2011Prii, Aug 20, 2019
    Last edited: Aug 20, 2019
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