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Keeps blowing water pumps, 3rd water pump, code p261b

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Brandon_P, Jun 25, 2019.

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  1. Brandon_P

    Brandon_P Junior Member

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    Hello all,
    I recently had my engine replaced and the car has been throwing code p261b. My mechanic has replaced the water pump 3 times now. Last week while driving the car stalled and threw code P261B, again.

    Prior to having the engine replaced my local Toyota dealer installed the first water pump because the prior one needed replacement. When they replaced it, they sent it back to my body shop and the car stalled on them. Toyota claims they "installed a fuse incorrectly" and that was the cause of the stall. Ever since they did this the car has not been right and kills water pumps. Typically the water pump lasts ~2 weeks (2,000 miles for me) before stalling and throwing code P261b. The last one lasted 9 days.

    The wiring is good and my mechanic inspected the fuse box and can't find anything amiss. Did Toyota fry my ECM?

    SM-N960U ?
     
    #1 Brandon_P, Jun 25, 2019
  2. Dxta

    Dxta Senior Member

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    I suspect there's a current surge in that circuitry. Its either there's a power short to ground.
    How did you know the integrity of the wire is intact?
    Can you check the fuse rating that was used by Toyota when they did a replacement?
    If you found nothing, then, you got to rip open those wires and check.
    Another reason could be that those pumps may not be OK.
    This is highly unlikely though.
     
    #2 Dxta, Jun 25, 2019
  3. Brandon_P

    Brandon_P Junior Member

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    The mechanic told me the wire is intact. I also watched him install the last pump (technically the 4th one installed) and didn't see anything amiss on the wiring. I haven't checked the fuse rating but my mechanic looked at it and said it was the correct fuse and it appeared fine.

    Where is the fuse location? I will check it out tonight.

    SM-N960U ?
     
    #3 Brandon_P, Jun 25, 2019
  4. Dxta

    Dxta Senior Member

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    The fuse is at the hood area. You'd see a black box kinda plastic. Pop that open, and you can see the various fuses there.
     
    #4 Dxta, Jun 25, 2019
  5. fotomoto

    fotomoto Senior Member

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    Brandon, I think you are referring to the electric inverter coolant pump. A "water pump" is an old school term for the one on the gas engine and is purely mechanical and thus won't burn out.

    You've got some sort of electrical issue that is blowing out those electrical pumps. Don't even think about trying to install larger fuses!

    GOOD LUCK!
     
    #5 fotomoto, Jun 25, 2019
  6. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    FWIW, I think Toyota refers to the engine coolant pump as "water pump".
     
    #6 Mendel Leisk, Jun 25, 2019
  7. jerrymildred

    jerrymildred Senior Member

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    On Gen 3 and newer, the ICE water pump is electrically driven. There are no belts in the engine bay. Also, that code is for the ICE water pump circuit.

    As for the fuse, that can't cause pumps or anything else to burn out; but it can ALLOW things to burn out if the fuse is too high of an amperage rating and the pump jams or is otherwise overloaded.

    Are you sure it's burned up? Or is it seized? Does the car have the right coolant and is it clean? If the coolant gets gunky or it there's debris in the coolant, the pump can seize. Also, I'm not sure what would happen if your mechanic replaced the Toyota SLLC with Prestone or something like that. I assume that the replacement engine was used. I wonder what kind of stuff might be in those coolant passages.

    I can't figure out installing a fuse wrong. There should only be one way to install a fuse. But it is easy to install the wrong fuse.
     
    #7 jerrymildred, Jun 25, 2019
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  8. Brandon_P

    Brandon_P Junior Member

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    The car is filled up with OEM coolant and runs until it gets up to Temp then stalls out because of the water pump not operating due to that water pump circuit code.

    None of the pumps that were replaced ever seized up all of them the issue with the circuit and threw the code after driving them approximately 2000 miles. No other issues with the car other than this

    SM-N960U ?
     
    #8 Brandon_P, Jun 25, 2019
    jerrymildred and Pluggo like this.
  9. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Are they OEM pumps, or?
     
    #9 Mendel Leisk, Jun 25, 2019
  10. fotomoto

    fotomoto Senior Member

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    Thank jerry, completely forgot about that improvement. Still stuck in the gen 2 world..... LOL
     
    #10 fotomoto, Jun 25, 2019
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  11. Brandon_P

    Brandon_P Junior Member

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    Yes, all OEM water pumps all brand new.

    SM-N960U ?
     
    #11 Brandon_P, Jun 25, 2019
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  12. jerrymildred

    jerrymildred Senior Member

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    Wow. That's really odd!
     
    #12 jerrymildred, Jun 26, 2019
  13. kc5dlo

    kc5dlo Active Member

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    Are the water pumps actually bad or are they replaced because of the code it sets off?
     
    #13 kc5dlo, Jul 2, 2019
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  14. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    ^ This. What criteria does the computer use to decide the pump is bad? Is it operating on false information? Betcha the answer is in the factory service manual...
     
    #14 Leadfoot J. McCoalroller, Jul 2, 2019
  15. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    You woke me up:

    upload_2019-7-2_15-41-17.png
    upload_2019-7-2_15-41-41.png

    See attachment for troubleshooting info:
     

    Attached Files:

    #15 Mendel Leisk, Jul 2, 2019
  16. Brandon_P

    Brandon_P Junior Member

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    Functionally they're fine according to my mechanic but they keep tripping the system so it won't drive because they are not turning on

    SM-N960U ?
     
    #16 Brandon_P, Jul 2, 2019
  17. Brandon_P

    Brandon_P Junior Member

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    #17 Brandon_P, Jul 2, 2019
  18. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    I just quickly assembled that, based on some skimming. If it's missing stuff or there's other references you need, just post and I'll look.
     
    #18 Mendel Leisk, Jul 2, 2019
  19. johnnychimpo

    johnnychimpo Active Member

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    I'm dealing with this. What did you end up figuring out?
     
    #19 johnnychimpo, Aug 28, 2021
  20. ChapmanF

    ChapmanF Senior Member

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    You can follow in this thread how you can watch how the water pump motor is being controlled in Gen 3.

    It looks like this when the car is asking for 50% (which is what you get if you select 'ON' in the Techstream active test). The top trace is what the ECM sends to the pump; the bottom is the pump tachometer signal back to the ECM (around 3300 rpm in this pic).

    [​IMG]

    In this one, I'm not using the Techstream test, but the cabin heat is turned on. You can see the ECM is asking for about 40%, and the pump is doing about 2730 rpm.

    [​IMG]

    You might find something funky in the signals to or from your pump if you look.
     
    #20 ChapmanF, Aug 28, 2021
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