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Check Hybrid System - not sure what to think...

Discussion in 'Gen 3 Prius Main Forum' started by JPV, Jan 3, 2022.

  1. JPV

    JPV Junior Member

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    Hello!

    Yesterday, after an 90 minutes of driving on the interstate, I got the "Check Hybrid System" warning with multiple idiot lights including the bright triangle. I lost the ability to accelerate, but luckily was right near a rest stop and managed to safely get off the road.

    I did a quick search here and by turning the car off and on, I was able to get rid of the Check Hybrid System and most of the idiot lights. Check engine stayed on, but went off eventually. I then proceeded to drive another 700 miles to my house!

    Today I read the codes and the only thing I had was P261B code - which looks to be engine water pump. I am really not sure what to think about this. Certainly if the water pump was having issues, I wouldn't have been able to drive for another 12 hours? When this error light came on, there was lots of snow and slush on the roads and changing lanes was an adventure...What do you all think I should do? I do have another 800 mile trip coming up at the end of the month, so I am inclined to change the water pump out, but it really just doesn't make any sense...could there be another explanation or
     
    #1 JPV, Jan 3, 2022
  2. bisco

    bisco cookie crumbler

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    that usually means you won't get heat iirc. if the code comes back, i would change it
     
    #2 bisco, Jan 4, 2022
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Dealership diagnostic?
     
    #3 Mendel Leisk, Jan 4, 2022
  4. ChapmanF

    ChapmanF Senior Member

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    P261B tells you that the water pump is underperforming. The code sets if the pump is doing less than 900 RPM.

    Whenever the ECM is giving you a water pump code, it also applies a special, lower, hard limit on engine temperature. This 105 ℃ limit only applies when a water pump problem is known to the ECM.

    [​IMG]

    What likely happened was that after 90 minutes on the interstate, your engine reached the magic 105 ℃ temperature. At that point, when the ECM knows of a water pump problem, there is no discussion, it shuts the engine right down on the spot. The car is left with nothing but the charge in the battery to get you safely off the road.

    The power management control ECU, which is kind of the orchestra conductor for the car, isn't even really in the loop when that happens. It will end up noticing the engine shut down and log a P0A0F code ("hey, for some reason the engine won't run"). That gives you your bright triangle.

    If you have any sort of scan tool or phone app that you can connect to the car and watch the engine coolant temperature, you can probably avoid a repeat by making sure never to hit 105 ℃ temperature before you have managed to get the water pump replaced.

    But by all means get the pump replaced promptly. It is no way good for an engine to be run with a dodgy water pump, even if you're careful to stay under 105 ℃.

    More information on the water pump's operation and the ECM's shutdown rules can be found in this thread.
     
    #4 ChapmanF, Jan 4, 2022
  5. JPV

    JPV Junior Member

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    Thanks for this info about how the ECU works to protect engine. Just to play devil's advocate - why didn't the engine reach 105C sometime during the next 700 miles after it stopped me? I didn't change driving style at all except I did take it out of "Eco" mode? Also, the "check engine" light stayed on for a while (maybe 2-3 hours) after the incident, but then it went out as well....
     
    #5 JPV, Jan 5, 2022
  6. ChapmanF

    ChapmanF Senior Member

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    I don't have much ability to determine what happened with me not there. But I don't know if you're planning to go very long after a water pump code without checking it out and repairing or replacing according to what you find.

    If you might, and you don't have an OBD-II tool that can monitor the coolant temperature to eliminate wondering about it in the meantime, getting one might be a good call.

    A lot of the time, coolant temp < 105 ℃ in normal driving.
     
    #6 ChapmanF, Jan 5, 2022
  7. JPV

    JPV Junior Member

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    I need to get one of those OBD tools for sure. I decided to change out the water pump just to be on the safe side - doing that today. If that doesn't solve the problem, I will come back to this post to update.

    I appreciate all the feedback! Thanks!
     
    #7 JPV, Jan 6, 2022
  8. JPV

    JPV Junior Member

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    I replaced the pump today - that is a pretty easy job! Gonna figure out how to see real time data now...
     
    #8 JPV, Jan 6, 2022
    bisco likes this.
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