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How Do I Test a Bad Water Pump?

Discussion in 'Gen 4 Prius Main Forum' started by PaulHeiser, May 23, 2023.

  1. PaulHeiser

    PaulHeiser New Member

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    I recently replaced a water pump. What happened was the coolant was blown out because of a heat exchanger malfunction at the cat converters, so the water pump was spinning too fast without any coolant on the propellers fins.

    I got an Aisin water pump, and the error code went away. I fixed the heat exchanger after going through the whole head gasket misdiagnosis routine (disassembled/reassembled engine), and the water pump error code is back on.

    I tested all of the pins on the water pump with the multimeter. It never showed any ohms.

    If I'm not mistaken, isn't that how to test bad electric parts? It has to show ohms to prove it's not faulty, right?

    Oh, I also tested the fuse and relay.
     
  2. PaulHeiser

    PaulHeiser New Member

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    What's weird about this one is that the car doesn't overheat when I drive it, but the pump doesn't show it's good with the multimeter.
     
  3. BiomedO1

    BiomedO1 Senior Member

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    Use a Bluetooth OBDII reader and sync it to your phone. Then download something like the Torque app. Monitor your ICE coolant temperature on hot days and in heavy traffic with a drained, empty traction battery. This will allow you to shut-down and allow the engine to cool down, before getting the CEL or over-temp lamp.
     
  4. PaulHeiser

    PaulHeiser New Member

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    My scanner says it's the coolant pump B that's out. But I pulled it off, and kept it plugged in, and then ran the motor a sec. The pump spins, so there's nothing wrong with the water pump as expected.

    However when I tested with the multimeter, no ohms showed on any pair of pins.

    So scanner and multimeter are wrong. It's a new pump too, so...and there was no overheating.

    Is it a different cooling pump in this car...like the inverter cooling pump?
     
  5. rjparker

    rjparker Tu Humilde Sirviente

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    I would start by checking the connectors and watching for coolant flow from the bottom hose of the reservoir when it warms up. But I would want to watch the coolant temp with a scanner. Verify it really is not overheating.

    A scanner is essential on any car but more so on a hybrid. Knowing the code is number one and knowing what the engine temperature is is number two.

    On a variable speed pump you have power and ground and two simple comm lines. You can verify the 12v and ground with a standard meter but it takes a oscilloscope or graphing meter to see the pulses on the other two lines.

    Since its a gen4 you need to download accurate test procedures and drawings for $25 from TIS.

    It is possible to ohm out the wiring and measure voltages under defined conditions. After the simple tests go to a dealer for an accurate diagnosis if it is not easily fixed. The third teardown is not the charm with head gaskets and overheating.

    https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti?_pageLabel=ti_whats_tis&_nfpb=true
     
  6. PaulHeiser

    PaulHeiser New Member

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    What exactly am I looking for on the TIS sight? I checked for manuals, but I didn't see anything that was specifically for testing this.
     
  7. rjparker

    rjparker Tu Humilde Sirviente

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    There are specific "Repair Manual" procedures that provide steps per code. You can download sections at a time as pdfs. Also detailed schematics "Wiring" with pins and colors.

    If its a pending code and you have verified it flows and isn't overheating, clear it and see if it comes back. The water pump gets pulses to set its speed from the ecm and provides pulses to feedback speed. If that control loop is open or shorted it will code but could still be operating.

    Four screenshots. Yours could be different.

    IMG_0272.jpeg
     

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    #7 rjparker, May 24, 2023
    Last edited: May 24, 2023
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    Attached is the engine cooling system section from the Gen 4 Repair Manual. It's from a "static" pdf copy, links broken, but hopefully has what you need for testing the water pump. Let me know if you need other pages.
     

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  9. ChapmanF

    ChapmanF Senior Member

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    There's more than one water pump error code, saying different things about the water pump. We can always help you best if you include in the post what code you are getting.

    No, it's not that easy. You have to understand any specific electric part in order to come up with a workable way of testing that part. This car's engine water pump uses a brushless DC motor with an electronic speed controller having a PWM input and a square wave tachometer output. There really isn't any of that where you'd see a meaningful ohms reading telling you if the thing is good or bad.

    You can find more about how the pump is powered and controlled in this thread. (It's about Gen 3, but it doesn't look like the pump is radically different. Pin locations in the fuse box have probably changed.)

    Some of the water pump codes (you still haven't said what code you've got) are about the RPM of the pump; there's a code for too high and a code for too low. Pulling it off and watching the pump spin may not tell you a lot, unless you've got a really good eye for RPM (and unless you are holding the pump in a volute filled with coolant).

    The thread linked above will show some ways you can test the pump if you have access to such equipment and really want to go that deep, but a lot of the time, just using a scan tool and seeing what codes are reported and maybe watching the target and actual pump RPM will be enough to spot an issue.
     
  10. rjparker

    rjparker Tu Humilde Sirviente

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    He says its a P261B
     
  11. PaulHeiser

    PaulHeiser New Member

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    Thanks for the info. I'll need it later.

    Basically what is wrong is that the computer has to run several drive cycles before it erases the pending code. It's only showing a pending code, therefore no check engine light is triggered. It's not a confirmed code, and it won't be basically since the computer will gather enough data to confirm the replaced pump is running.

    I'll still do a live graph scanner test to see what the coolant temp is doing.
     
  12. ChapmanF

    ChapmanF Senior Member

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    Woops, I never saw that quote; link says "conversation not found" for me. Private conversation?

    That's the pump RPM too low code.
     
  13. Mendel Leisk

    Mendel Leisk Senior Member

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    I've been alerted the doc I uploaded above is incomplete; I'll take another look.
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    Maybe cooler heads can have a look at the attached. My "manual" is a cribbed copy, kinda jumbled.
     

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  15. PaulHeiser

    PaulHeiser New Member

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    Thanks for the docs.

    So the car's back running strong. This all started as just a heat exchanger default obsolescence by-pass job...which got side tracked into the weeds. I broke it down once to get in a new head gasket. I broke it down twice to take the block and head to the machine shop. I even broke it down a third time because after I got it back together, and I drove it a bit, I noticed oil seeping from the timing chain cover. Basically what happens is when you put on the timing chain cover with the sealant around the edges, the cover is probably going to touch somewhere at the bottom to something, and that removes some sealant off the edges. So on the last try I used 2.5x the amount of sealant around the whole lower portion of the cover.

    I learned so much this whole month on a total misdiagnosis to begin with. Thanks, all.
     
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  16. AmazingFacts

    AmazingFacts Member

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    Hi Paul, how many miles were on your car when the head gasket blew? Did you ever did a HG repair on a gen 3 Prius? If so, was it mostly the same procedure?