Check Engine/Hybrid System, code P261b, but pump still turns on?

Discussion in 'Gen 3 Prius Main Forum' started by gradyoactive, Dec 2, 2019.

  1. gradyoactive

    gradyoactive New Member

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    Last week I was driving my 191k 2010 Prius in a heavy rain storm, and I stupidly plowed through a massive puddle going 20 mph. My plastic underbody engine cover had been partially damaged for months, by the way. Later that night, the Check Engine Light came on while I was driving 65 mph uphill, and the Check Hybrid System warning also lit up a few seconds later, along with the Exclamation Triangle flashing. I felt my engine shutting down, and I was lucky to make it off the exit and pull over. Then as I idled and googled frantically, my dash lights flickered and the car shut off. I tried starting it back up a few minutes later, but the wipers went extra slowly, so I shut if back off and waited 15 minutes or so, and it powered on again enough to limp a couple miles home.

    I then read the OBDII codes and got P261b, which is a malfunction in the electric water pump cooling the engine, and after reading some PriusChat threads I ordered a new one. The next day, the codes were gone. I topped up the coolant because it was a little below the Low mark. The car seemed fine for a couple days until the error lights happened again. But I had been driving it normally, accelerating pretty quickly to test it while monitoring the coolant temp with my OBDII scanner. It was actually pretty difficult to get the temp any higher than 200 F in the cold weather.

    When the errors came back I shut the car off again, and cleared the codes. The next time the CEL came on a day later I just drove as slow as I could, and the Hybrid System warning never came on. CEL went away on its own after driving a few miles and shutting the car off. I've been avoiding accelerating ever since. So far so good but it's very annoying going so slow.

    I got the new pump in the mail, but before I was going to install it, I used my Techstream to test if the water pump still works using the active test, and it does actually still turn on. But the RPM it runs at is higher than the target RPM. With a target RPM 3175, Techstream measures 3625. And when the target is 2475, it measures 2900. The p261b code is only supposed to show up if the RPM is less than 900, or so I've read.

    I have a few questions:

    Does that target vs measured RPM discrepancy mean the water pump is still broken or is that normal?

    If my pump still turns on when I tell it to, why isn't it turning on properly while I'm driving? Could there be some kind of communication error between the engine/thermostat, etc. and the pump, that would require a different solution than just replacing the pump?

    Or is the pump working fine except the car thinks it isn't for some reason (some kind of sensor error?) and mistakenly shuts down preemptively?

    I'd rather not waste installing the new pump if it won't fix my problem. And I'd rather not get it professionally fixed and throw too much money at this old car that's probably only worth a few grand anyway. I was hoping to make it to 240k or so (which is a pretty modest goal but I drive it pretty hard, 25k miles/year through Boston weather and potholes, and I also potentially damaged the engine ~10k miles ago by stupidly letting the oil run low).

    Sorry if this has been answered before. I couldn't find a definite answer for this particular situation (p261b but pump still hitting 3600 rpm). Let me know if I'm forgetting any important details. Thanks!
     
  2. hotelprisoner

    hotelprisoner Member

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    I recall a thread on here somewhere where someone indicated they had performed the same tests and also had a higher RPM then commanded. After tearing out the pump it was discovered that the motor shaft had sheared or separated from the impeller and the motor was now in free spin resulting in the higher RPM now that it was unloaded.


    iPhone ?
     
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  3. gradyoactive

    gradyoactive New Member

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    Interesting. So I guess I should remove the pump and take a look. Thanks!

    Also, am I damaging my engine by driving on it for a few days before fixing it? Or does it shut itself off before permanent damage occurs?
     
  4. gradyoactive

    gradyoactive New Member

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    I decided to save $42.50 by buying the same water pump from a different seller, but it won't get here for a couple days. In the meantime I'll be driving slow and monitoring the coolant temperature with an OBDII scanner.

    At what temperature will the engine get damaged from overheating? It's been cold in Boston lately, and the coolant temp is usually in the 175-195 degree F range. If I make sure to keep it under, say, 200, will I be OK?

    Note that I only got the P261b water pump malfunction code, not any overheating warnings. Could I still be damaging something without overheating?
     
  5. ASRDogman

    ASRDogman Senior Member

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    If the coolant is not flowing, the engine will overheat if you drive it. You are taking a huge risk.
    By the time the sensor tells you it's overheating, it has already been overheating!
    Do you have money for a new/used engine? Do you have the time and skill to replace it?
     
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  6. Johnny Cakes

    Johnny Cakes Active Member

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    If the motor shaft has sheared or separated from the impeller then it would seem that no coolant is moving through the system. You would only getting a temperature reading at the one specific point where the sensor is, meaning that you wouldn't really know what the temperature is elsewhere. Really bad things could be happening before the sensor light comes on, if it comes on.

    Ambient outdoor temperature has only a minimal effect on engine temperature, given that the heat generated during the fuel combustion process is so high. Also, whereas an air-cooled engine is designed with heat sinks and air flow for cooling, the Prius engine is sealed off.
     
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  7. Georgina Rudkus

    Georgina Rudkus Senior Member

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    The major cause of blown head gaskets is overheating. Years, ago, cast iron engines could take several minutes at 1100 degrees F.

    Current aluminum engines become "mushy" at 500 degrees F,
     
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  8. hotelprisoner

    hotelprisoner Member

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    iPhone ?
     
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  9. gradyoactive

    gradyoactive New Member

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    Thanks for all the replies. I'm an idiot for not realizing the coolant temp would be lower than the engine temp when the pump isn't working properly. You successfully scared me into finally installing the new pump. It was pretty hard to get some of the bolts off, especially in the freezing cold, but I got it done eventually.

    When I took the old pump out, it looked totally fine (no dry pink residue, so no leak), and felt/spun exactly like the new one. Luckily I saw hotelprisoner's youtube video, and then tested the pump using my Techstream. It would spin for a second and then sputter and stop spinning, then spin, etc. So something must have sheared off inside.

    The hardest part of the whole job was getting access to and especially twisting the radiator drain with virtually no space for my frozen hand. My hand and wrist are all cut up now.

    One last thing: When I was installing the new pump, I noticed that the little ribbed tube that comes from the top left of the engine and connects down to the bottom of the coolant tank was split open a little in a couple spots. I figured that was a bad thing, so I wrapped it a couple times with duct tape until I figure out what it is and how to fix it.

    What does that tube do? Is it supposed to be totally sealed or is it intentionally cracked open a little? It's a truly atrocious design if it is meant to stay sealed; it's basically perforated along the side. Is it easily replaceable?

    Here is a pic of the tube (the one that looks ridiculously duct taped):

    Thanks!
     

    Attached Files:

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  10. ChapmanF

    ChapmanF Senior Member

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    That's an electrical ground wire, with some corrugated plastic tubing slipped over it to protect it from rubbing.

    It'll be fine without the duct tape.
     
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