P3190 & P0420 - Sudden Limp Mode (P0A0F) On Freeway

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by SCBPrius, Mar 12, 2025 at 8:29 PM.

  1. SCBPrius

    SCBPrius New Member

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    Long-time forum lurker, and now have something worthwhile to query about.

    2012 - Prius Two - 310k miles
    Engine replaced at ~185k for standard headgasket issue
    Fuel Pump Replaced at ~280k miles

    Vehicle has had a sudden & intermittent check hybrid system warning light and kicked into limp mode, this has historically occurred (2-3 times) and while on the freeway, driving at freeway speeds. Only codes showing were P3190, P0420 and P0A0F. Second code is likely related to clogging cats (they are original) so my focus had been on P3190 as I thought P0A0F was a generic hybrid error code (caused by the P3190).

    I've dug into things slightly, and the throttle body had some carbon buildup, but wasn't totally covered, and because this issue has occurred while under freeway drive load, this didn't seem likely to be the issue. Also checked the EGR ports inside the intake manifold, but they were unclogged and looked relatively clean as well.

    Checked under oil cap for any signs of headgasket issue, and I don't appear to be using any coolant (yet), though the exhaust does potentially smell a bit rich.

    After the tow, and clearing the P0A0F it starts up and drives, but there's obviously something which caused the P3190. Any suggestions for likely culprits? I wondered if it could be the Fuel Pump again, shop might have used a "budget but OEM spec" option that time... My searching on the forum corroborates my guestimate about the fuel pump being the issue, but seems surprising it would fail that quickly.

    Would appreciate any guidance!
     
    #1 SCBPrius, Mar 12, 2025 at 8:29 PM
  2. MAX2

    MAX2 Active Member

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    P0A0F
    If an engine malfunction occurs, an engine malfunction signal is the ECM to the power management control ECU (HV CPU) . When the power management control ECU (HV CPU) receives this signal, it sets a DTC and performs fail-safe control.

    This error code has subcodes that could be read in a workshop with a special scanner. Subcodes could accurately indicate the source of the problem.

    But in general, yes, while driving, these could be problems with fuel supply, clogged filters and problems in the fuel pump.
    I would not exclude a small amount of fuel remaining in the tank.
     
    #2 MAX2, Mar 13, 2025 at 3:09 AM
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  3. ChapmanF

    ChapmanF Senior Member

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    That's pretty much right. P3190 is set by the Engine Control Module, the ECU that has direct responsibility for the engine. P0A0F is set by the power management control ECU, which is kind of the orchestra conductor for the car. It said "hey ECM, I'll crank the engine now if you'll make it go", and cranked it, but it didn't go, and the P0A0F kinda means "I don't know what the story is, but I asked the ECM to make the engine go and that didn't happen."

    So P3190 is the information you've got from the ECM, which is in the best position to know. But people are still frustrated that P3190 is not a more specific code. It means "hey, I calculated how much torque the engine should be making right now but it's making less than a fifth of that", which tells you the engine is running like cr@p for sure, but doesn't tell you a lot about why.

    It's one of those deals where a lot of different things can make a gasoline engine run like cr@p, and the human has to kind of dust off the old gasoline-engine diagnosis cap and start checking them all off the list.
     
    #3 ChapmanF, Mar 13, 2025 at 9:34 AM
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  4. SCBPrius

    SCBPrius New Member

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    Thank you!

    On most recent instance, fuel was filled to top (by me) that morning at the "regular" gas station we use for all our vehicles, so that aspect is likely ruled out.

    Dr Prius app and a Veepeak bluetooth OBD2 code reader wouldn't give the required additional color (the degree of detail) on those codes which you mentioned, right? I presume that would require a more professional Autel level type tool?

    If so, I'm effectively at the point where I either, 1) throw parts at it and hope I get lucky, or 2) get a real shop to do some diagnostic work
     
    #4 SCBPrius, Mar 13, 2025 at 10:48 AM
  5. SCBPrius

    SCBPrius New Member

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    Yes, my automotive diagnostic cap has effectively reached its knowledge and experience limit with how much I've done to this point, and without additional data from a more advanced scan-tool, it seems there's not much more I can personally do other than throw parts at it and guess.
     
    #5 SCBPrius, Mar 13, 2025 at 10:51 AM
  6. MAX2

    MAX2 Active Member

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    Trying to replace random hardware is a bad idea.
    Error code P3190 can have many problem areas. A more advanced scanner is needed that can read freeze frame data when an error is recorded and narrow down the suspects based on this data.
    This is directly indicated in almost half of the cases of error occurrence.

    Tech Tips
    Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air-fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
     
    #6 MAX2, Mar 13, 2025 at 12:15 PM
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