Low Coolant and Now P3191

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by TheCoachStone, Oct 8, 2025 at 6:28 PM.

  1. TheCoachStone

    TheCoachStone New Member

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    Hey guys, I own a 2013 with 200k. Yesterday I was driving and noticed white mist from the right side of the hood. I stopped and found a pinhole in a y pipe that runs in the front of the car from the coolant reservoir to the front of the engine and then to some of the hybrid system. The car did not overheat and it did have coolant left in it. I had it towed to a shop I trust, and they replaced the tube and y piece. But now the car wont run. It cranks and runs for a few seconds, but then it cuts off and says check hybrid system. The only code is P3191 - which I found out could be the throttle body, mass airflow sensor, or fuel pump. I'm getting fuel and enough air to run the gas engine, so what am I looking at? Does engine coolant go into the hybrid system separate from the hybrid engine coolant? It is failing during its warm-up sequence, so is there a chance something in the hybrid system needs to be reset or checked? Or could the MAS have gotten some mist on it and caused it to fail? The engine does not run rough. It has a fairly new 12v and it was tested. The hybrid battery is low but still shows one bar.

    Thanks in advance.
     
    #1 TheCoachStone, Oct 8, 2025 at 6:28 PM
  2. rjparker

    rjparker Tu Humilde Sirviente

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    Probably somebody failed to reconnect a sensor - first I would check is the maf on the air box.
     
    #2 rjparker, Oct 8, 2025 at 8:03 PM
  3. ChapmanF

    ChapmanF Senior Member

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    I'd kind of expect a P0102 code if the MAF got left unplugged.

    Sometimes diagnostic progress can be slowed by starting with some overly-specific idea of what a code is telling you.

    The P3191 code in gen 3 means the same thing as P3190, with one added element. P3190 means that the engine was caught producing (for whatever reason) less than a fifth of the torque it should have been producing at the time, and it becomes P3191 if this was while the engine was being started.

    So it's really saying "this engine is running mighty poorly" and someone needs to put on an old-school gasoline engine diagnostic hat and check out all the usual suspects, which are all the things that affect fuel mixture, compression, or spark.

    Maybe, somewhere in the area where the work was done, someone created an intake leak, such as by leaving a vacuum hose off.
     
    #3 ChapmanF, Oct 8, 2025 at 9:14 PM
    BiomedO1 likes this.
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