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P261B code. Could I have damaged a water sensor if there is such a thing?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by chuckiechan, Aug 25, 2022.

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  1. chuckiechan

    chuckiechan Member

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    I did a complete EGR clean out less than two tanks of gas ago. Everything went well.

    EXCEPT when refilling the radiator, I spaced out and poured about three ounces of synthetic oil in the radiator reservoir. I have been pulling it out with a turkey baster from the top tank as it floats to the surface, most of it is gone.
    So today the CHECK ENGINE light came on Code P261B. No other lights came on to indicate heat. No obvious noise I can detect from the pump.
    BTW, it has been very hot is Sacramento.

    Sooo…
    A WATER SENSOR was mentioned, but not a lot of info. Could the motor oil have damaged it?
    I am going to do a radiator FLUSH, hoping that helps.
    Lastly, on the EGR job I filked the radiator from the overflow tank. I didn’t see a radiator cap on the radiator itself.
    Suggestions?

    Sorry to ramble… ;)



    iPad
     
    #1 chuckiechan, Aug 25, 2022
  2. ChapmanF

    ChapmanF Senior Member

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    There are a couple water temperature sensors, but you're unlikely to have damaged them, and they aren't what a P261B code is about, anyway.

    P261B means the electrically-powered engine water pump was doing less than 900 RPM when the engine control module wanted it to pump faster than that.

    There's a plastic impeller in there that sometimes swells or splits and becomes harder to turn, slowing the pump down. It's possible having the wrong stuff in there might have accelerated that deterioration of the plastic, but it's also possible it just happened to be about that time for the water pump. You haven't mentioned the mileage on the car.

    You might be used to cars that have a radiator filler and an overflow bottle. Your Gen 3 liftback doesn't. The bottle over by the inner fender isn't an overflow bottle, it's a "degas bottle" and it is the only filling location for the system.

    You'll notice it has lines marked LOW , FULL, and B. B is above even FULL, and it is the line you use when burping the system. If the system has been drained, you fill it all the way to B, put the cap back on, start the engine, warm it up to full operating temperature and run it that way for several minutes, shaking various radiator hoses (while keeping your fingers out of the fans). Then you turn the engine off, wait for everything to cool, and notice the level has normally gone right down to FULL, just like the engineers knew exactly how much air would burp out.

    You'll have another chance to practice that after replacing the water pump. :)
     
    #2 ChapmanF, Aug 25, 2022
    Last edited: Aug 25, 2022
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  3. chuckiechan

    chuckiechan Member

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    It has 90,000 miles.
    Thank you for you explanation. Any suggestions on safe chemicals to flush the system to remove the oil?
    It looks pretty tight in there… I’ll scare up a video.
     
    #3 chuckiechan, Aug 25, 2022
  4. ChapmanF

    ChapmanF Senior Member

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    Seems like 90,000 is early for a water pump to poop out, but you could just be lucky, I guess.

    Also seems like early-ish mileage for EGR cleaning ... it would be interesting to see your before-cleaning and after-cleaning EGR flow test results if you saved those.
     
    #4 ChapmanF, Aug 25, 2022
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  5. chuckiechan

    chuckiechan Member

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    It’s possible I killed it. I’m going to flush it twice because of the oil. I’ll erase the code, and if it pops up again, I’ll change the pump.
    I may change it anyway. I plan to sell it so I don’t want shaft anyone. Been poor & know how tough it can be when bleep happens.
    So far the dealer did the ECM (?) and the brake booster on warranty. So I did the ERG (totally clogged), manifold, plugs, PCV, cleaned TB, MAP, MAF, etc. per what people recommend here.
    Thanks again for your info.

    EDIT: BTW, did the code come up because the pump wasn’t running at specs for the temperature?
     
    #5 chuckiechan, Aug 25, 2022
  6. ChapmanF

    ChapmanF Senior Member

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    People often work on their EGR systems and then report qualitative judgments of the condition like that.

    For the PriusChat community, it is really useful to also report the EGR flow self-test numbers from before and after the work. Helps us kind of map out how common qualitative judgments at different mileages map out into actual flow.

    Had you received a P0401 insufficient-flow code before doing the work?
     
    #6 ChapmanF, Aug 25, 2022
  7. chuckiechan

    chuckiechan Member

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    I’m just Joe Six-Pack. I don’t have access to tech stream.
    We used a simpler reader. FIXD, I think.

    Back to the water pump. Did the electronics say the pump output was not up to specs and sent a code?
     
    #7 chuckiechan, Aug 25, 2022
  8. ChapmanF

    ChapmanF Senior Member

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    P261B means the electrically-powered engine water pump was doing less than 900 RPM when the engine control module wanted it to pump faster than that.

    The pump doesn't "send" the code. It has a tachometer output. The ECM reads that, and decides when to set the P261B code.

    Techstream isn't needed to get EGR flow numbers. "Mode 6" monitor test results are a standard OBD-II feature.
     
    #8 ChapmanF, Aug 25, 2022
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  9. chuckiechan

    chuckiechan Member

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    I flushed the cooling system twice, and rinsed twice, both times putting two hours or so on the road in pretty hot weather.
    The CEL was off before I even started flushing and never came back on.
    So what ever happened that caused the code must have resolved itself.
    Anyway, Thanks again for the help!
     
    #9 chuckiechan, Aug 28, 2022
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