Water Pump Relays and Fuses

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

  1. echobox

    echobox New Member

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    Hello!

    I have been stalking this site and using all the great information here to do many repairs on my 2010 Prius since 2017. So thanks for all the help already.

    What I am currently struggling with, I can't seem to get the info I'm looking for. Bought the car used with 217K miles and currently has 267K. Got the P261b error code and car glided to a stop at the side of the road. Had it towed home, ordered a new AISIN water pump and thermostat from Amazon which are arriving today. Old one was removed yesterday and it still turns though not smoothly. Was hoping it was dead seized.

    From what I have read here, water pump is the probable cause though I should have checked relays first. I have been struggling with diagrams showing relays from the Chilton's Library through my library and other diagrams online. The problem I am having is deciphering which relays marked "Cooling" or "Fan" are for the Cooling system (which I assume these would be) and which ones are for AC cooling. Can anybody point me to a document or thread in which the relays and fuses on the 3rd Gen Prius are defined? Or even a source that shows a diagnoses from start to finish when dealing with P261b (ie. Step 1, Check relay R1... etc).

    Thanks in advance!
    Jason
     
  2. AzusaPrius

    AzusaPrius Senior Member

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    Just throw the new pump and thermo on and reset the codes.

    You will be good to go after that.
     
  3. ChapmanF

    ChapmanF Senior Member

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    This is from the first page of the P261B writeup in the repair manual (more info):

    P261B.png

    As long as you've taken the old pump off and found it "still turns though not smoothly", you've probably already found why its RPM was too low, and might not bother with following the rest of the workup, unless you found the new pump to still have a problem.

    If you do end up wanting to go through the whole workup, it's all there, including the circuit diagram, on that page and the 13 pages after it.
     
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  4. echobox

    echobox New Member

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    I would love to have access to the repair manual for this car. But I don't.

    The reason I asked the question in the first place was because the new pump and thermostat and coolant ended up costing around $300. I wanted to know, before putting these in, cheaper steps that could be troubleshot beforehand. I love a good step by step troubleshooting guide, but I can't seem to find one for this problem. Like I said, just a list of which relays affect the cooling system would be helpful. From diagrams I've found online, it seems to be at least R1, R2, and R4. But there are also several fuses labeled "Electric cooling fans" which could be anything.

    Luckily, when the new unit arrived, there was a noticeable difference in the way the propeller spun vs. the old unit, so I went ahead with the exchange. So far, the code has gone away but the outdoor temps here are in the mid 20s so the engine fans are not kicking on. The temperature from my scangauge got up to 180F. I think I read in another post, Chapman, that you said they should kick on at 95C (approx 203F) so I'll have to drive it more and see?

    Thanks for the support!
     
  5. AzusaPrius

    AzusaPrius Senior Member

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    The thermostat starts to open at 180F and at 204F it is fully open but you shouldnt get to that temp with ease.

    The normal temps even in your weather should fluctuate between 180-195F.

    Hopefully the temps never pass 204F as this will cause damage to the engine.
     
    #5 AzusaPrius, Jan 26, 2022
    Last edited: Jan 26, 2022
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  6. ChapmanF

    ChapmanF Senior Member

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    Hmm, your profile says Kansas. I don't know whether you guys are thinking of seceding, but as long as that hasn't happened yet, I think techinfo.toyota.com should be accessible to you, as well as some of the other alternatives that Elektroingenieur described here.

    The Gen 3 cooling fan fuses are in a funky three-fer fuse you will see in the fuse box (the third in the three-fer is the heater blower). In this photo you can kind of see where the three-fer fuse isn't (because I pulled it out to stop the fans from running so I could achieve higher engine temps for the test). The fuse box cover has the labels.

    [​IMG]

    There are three relays controlling the cooling fans, and one supplying power to the water pump. I know I've seen posts here on PriusChat containing those sections of the diagram.

    You had a P261B code, pump RPM too low, right? There aren't any special temperature conditions for testing that. You put the new pump in, the ECM sees it turn the right speed, code goes away. Easy-peasy.

    If you really want to see the cooling fans run, you can usually get the engine temp high enough if you just sit in Park and hold the go pedal down for a while. In very cold weather you might still have to be kind of patient. Having a temperature readout to watch helps, so you can at least see the progress, as slow as it is.
     
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  7. echobox

    echobox New Member

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    Drove the car for over an hour yesterday and temp stayed within180-190. So, all good there. Thanks for the temp warning, I will continue to keep an eye on that while driving, especially as the weather warms up! Isn't there a scangauge setting/OBD reading that monitors if the thermostat is open or not? I'll have to look into that to watch too.


    Lol, we're too sedated on hamburgers and Jesus in Kansas to secede. Believe it or not, I looked at most of the sources on the Elektroingenieur post before I posted here, even downloaded and combed through a few but either they didn't have what I could use or I'm not smart enough to read them. When I searched the techinfo site, no repair manual came up. Just owner's manual, quick reference, USB guides, etc. I didn't create an account, so maybe I need to do this? If so, from the looks of it, they charge for the repair manual?

    Not sure what you mean by a "three-fer" (sorry). Do you mean fuses 36,37,38 as a single fuse? Of which in the photo the bottom is in line with the bottom of the oscilloscope? Those three are labeled "CDS Electric Cooling Fans, RDI Electric Cooling Fans and HTR Air conditioning system."

    In your photo, the two blue relays at the top right (R2 and R4) are "Cooling Fan" relays with R1 (hidden behind the oscilloscope) labeled "Cooling System (ENG W/P) and R8 (the rouge one at the bottom right of the box) also labeled "Cooling Fan (Fan No.2). Are these the 4 you are referring to?

    So the question would be, between the "three-fer" fuses and the 4 relays, is that the total of all relay/fuses connected to the engine cooling system? At this point, I'm asking for anyone who might stumble upon this post. You are right, I put the pump in and the code went away and everything seems okay at this point for me. But if I would have known what relays/fuses to check before dishing out $300 (and a few days of very cold labor) I would have done that first.

    Thanks for your help!!
     
  8. AzusaPrius

    AzusaPrius Senior Member

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    It was the pump the whole time and you would have wasted time poking around fuses, so dont feel so bad because if it was any fuse, you would still have a problem.

    Still want to poke around and see what actually would happen or codes, then just pull those fuses and find out.

    When not using the Dr. Prius App, I use this simple App.
    Just a coolant temp monitor and you can set an alarm at any temp you want, cost I think $1.50 in the playstore.

    This gives me assurance that I am not overheating at all.
    Believe me you will never know otherwise and by the time/chance that you actually see the red warning light, damage is already happening. Screenshot_2021-10-31-14-14-52-1.jpeg
     
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  9. ChapmanF

    ChapmanF Senior Member

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    Yes, I'll go take another look at the wiki page, maybe it needs an edit to make that clear. (I thought that was in there already.) Twenty bucks if you sign up for TIS directly. If your friendly public library subscribes to one of the downstream services, they could have it for you for free.

    In other posts, you seem to be interested in ways to avoid spending $300 unnecessarily on a repair, so in perspective, $20 equipping yourself with the information to do that seems pretty accessible.

    Yep, them's the ones.

    Yes, that right there is one of my favorite things about the repair manual and wiring diagrams. The more of my car repair I can do from indoors in a comfy chair with a nice mug of something nearby, the better. :)
     
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  10. echobox

    echobox New Member

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    Missed that, but $20 for 2 days usage... :mad:

    The Alldatadiy seemed like a better deal but their prices have changed: $60 for a year, $130 for 3 years.
     
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