P261b OBD code. Coolant pump problem

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by IamPrius, Jan 1, 2021.

  1. IamPrius

    IamPrius Junior Member

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    At just over 242300 miles up popped the second check engine light my car has had, this time code P261b, means there is a problem with the coolant pump, the wiring or a relay. I checked the wires, no fraying or loose connections. I did not check the relays. I did notice the coolant was rather low, like to the bottom of the reservoir. I used the Torque app to clear the code to see if it would reappear. It did the next day. As I was driving around the coolant temp never got above 195 F. When I got home I did more sleuthing on the 'net. One article I read stated that if the coolant level is low it could draw air into the system and cause the code. So I bought the proper coolant and filled the reservoir to the proper level. It has been eight days now and the code has not reappeared and the coolant temp does not get above 195 F. Seems I solved that problem, but now I wonder why the coolant was low.
     
    #1 IamPrius, Jan 1, 2021
    Last edited: Jan 1, 2021
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  2. jdenenberg

    jdenenberg EE Professor

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    When was the last time that your coolant was drained and refilled? When my dealer did that job, they failed to completely eliminate all the air in the system. Driving my 2004 Prius a while cleared out the air and left me with a low coolant level.

    JeffD
     
  3. IamPrius

    IamPrius Junior Member

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    Have not done the coolant changes yet.
     
  4. jdenenberg

    jdenenberg EE Professor

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    It was due at 100k miles and again every 50k miles thereafter.

    JeffD
     
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  5. ChapmanF

    ChapmanF Senior Member

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    Is this post about the 2016 shown in your profile?
     
  6. IamPrius

    IamPrius Junior Member

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    Of course. If it wasn't I would state that.
     
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  7. Mendel Leisk

    Mendel Leisk Sand Pounder

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    What's the consensus on the water pump here: preemptively replace every 100K miles? Or not soon thereafter? Thermostat too? @Raytheeagle ?


    Too many questions, lol.
     
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  8. IamPrius

    IamPrius Junior Member

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    Well, I have 2432xx miles and have not replaced the water pump or the inverter. If it ain't broke, don't fix it.
     
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  9. jdenenberg

    jdenenberg EE Professor

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  10. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Or the coolant?? :eek:
     
  11. ChapmanF

    ChapmanF Senior Member

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    Confirmation is good. You'd be surprised how many posts are from people having more than one car and neglecting to specify which. 242k is a pile of miles for a 2016.
     
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  12. IamPrius

    IamPrius Junior Member

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    I talked to the service manager at Toyota about it. Says they see cars all the time with higher mileage and/or older than mine with the original coolant and no problems at all.
    That does not mean I will not ever change mine out. Since I just bought a gallon I feel I will be doing mine soon.
     
  13. AzusaPrius

    AzusaPrius Active Member

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  14. IamPrius

    IamPrius Junior Member

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    Maybe it is, maybe it isn't. I'll change it when it goes bad.
     
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  15. ChapmanF

    ChapmanF Senior Member

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    My calendar/mileage date for the coolant would have been last year, but I had a bunch going on at the time so I dipped a test strip in and it came out fine so I spent the time on other things. When the weather warms up again I suppose I'll dip another strip, or just go ahead and change it.

    The pumps do seem to have an awkward failure mode possible, where the impeller comes apart and then the pump rotates easily without moving coolant. In 2010 there was a trouble code for pump RPM too low (that's what P261B is), but none for RPM too high, which is what happens when the impeller is busted. So in a 2010 you could have your pump thoroughly busted, not cooling your engine, and get no trouble code to tell you that.

    Apparently a code for RPM too high was added in 2011 (P148F). I would (nice person)-u-me that a 2016 has both codes, but it would be better to check the manual.

    What puzzles me in this thread is how a low-coolant situation could have led to a P261B, as the first post suggests. I would expect, if anything, a P148F if there was such low coolant the pump was slugging air.

    I have one nutty speculation that I have not yet had any time to test. In another post where the impeller busted, the Techstream-reported pump RPM was somewhere in the low 6,000s (I think full speed is normally 3,000-something when the pump is really pumping). It was a 2010, so no P148F code, so no trouble code at all logged, at least for low-6,000 RPMs.

    The possibility I'm wondering about (again, I've not tested this at all) is whether the ECM's pump-RPM scaling allows the RPM to wrap back to "zero" above some maximum RPM, such as, let's just guess, 6,553.5. That might allow, in some cases, an over-revving pump to set the under-revving trouble code.

    Still, in any car that has the tailor-made-for-over-revving P148F code, I would expect that one to show up first....
     
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  16. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Low coolant and 242k miles: ever cleaned the Exhaust Gas Recirculation and Intake Manifold?
     
  17. AzusaPrius

    AzusaPrius Active Member

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    So once you get that code P261B
    It is time to change it out, trust me.

    The reason for low coolant is because it is turning to vapor in pockets because the pump is not circulating the coolant as it should.

    Hence low coolant and you will still get the code again.

    You will not like the outcome of total shut down when it completely fails.

    Posted via the PriusChat mobile app.
     
  18. royrose

    royrose Senior Member

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    That's generally my philosophy too, but at 240,000 miles some maintenance if you want the vehicle to last much longer is in order, especially since replacing the coolant pump is not that difficult or expensive.
     
  19. IamPrius

    IamPrius Junior Member

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    Had not thought about hot spots. 8 days and counting so far w/out any codes. Temp does not get above 195 F and cools off pretty good when coasting.
     
  20. IamPrius

    IamPrius Junior Member

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    No.
     
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