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Engine Coolant Pump RPM Dropping to Zero

Discussion in 'Prius c Technical Discussion' started by Dr Usman Nawaz, May 17, 2017.

  1. Dr Usman Nawaz

    Dr Usman Nawaz New Member

    Joined:
    May 17, 2017
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    Location:
    Pakistan
    Vehicle:
    2014 Aqua
    Model:
    N/A
    Hello

    Recently imported Aqua 2014 from Japan, it is 18000 km driven

    On import its Engine check light was ON, Get it Scanned, and P261B Coolant Water Pump Malfunction code appeared... Mechanic asked to change the pump... We have changed 4 different pumps but engine check light comes on again and car takes heat... by connecting terminal to pumps outside car, all pumps were functioning...

    Then checked the RPM of water pump on scanner, it start with 1200 then goes to 3300 and then drops to zero and pump stopped... it happened to all four pumps...

    Then changed the ECM (Computer) of car, but the problem persisted...

    Checked terminals and Fuse box, all were ok...

    Now mechanic is suggesting that we are ignoring some important thing, all pumps are working outside car but drop rpm to zero when fixed in car... there might be some very minor electric issue like bad terminal, or loose grips or rust etc... But still we are facing this issue in our Aqua 2014...

    Can someone guide what should we do now...?????
     
    #1 Dr Usman Nawaz, May 17, 2017
  2. vincent1449p

    vincent1449p Active Member

    Joined:
    May 24, 2004
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    Location:
    Singapore
    Vehicle:
    2012 Prius c
    Hi Dr Usman Nawaz,

    This is what the Repair Manual says about P261B:

    "The ECM calculates the speed of the engine water pump assembly using a duty cycle signal the engine water pump assembly. When the speed of the engine water pump assembly becomes less than 900 rpm while it is operating, the ECM detects the malfunction and stores DTC P261B.
    The engine water pump assembly operates steplessly based on a duty cycle signal the ECM. If actual drive duty cycle ratio does not correspond to the target drive duty cycle of the engine water pump assembly, the ECM detects the malfunction."

    Engine Water Pump circuit.jpg

    It seems like ECM is trying to command 1200 & 3300 RPM at WPO(29) to SWP(4) but it did not receive back the expected target RPM from the Engine Water Pump Assembly NWP(2) to WPI(28), that is why it drops to zero and hence the DTC.

    If I were you, I would check for open circuit between ECM and Engine Water Pump Assembly, esp. pin 28 to pin 2 and also both are not shorted to ground.

    Vincent
     
    #2 vincent1449p, May 18, 2017
  3. Former Member 68813

    Former Member 68813 Senior Member

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    Oct 3, 2010
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    Vehicle:
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    It was my understanding one should not spin water pumps dry, even by fingers. they have to be wet for seals to function properly. not sure if that kills your pumps though.

    does the engine overheat?
     
    #3 Former Member 68813, May 18, 2017
  4. Stephen J Nesbitt

    Stephen J Nesbitt New Member

    Joined:
    Nov 8, 2019
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    Vehicle:
    2010 Prius
    Model:
    III
    Did you ever find out what caused this. I changed pump and ECU. The ECU was bad. Found refurbished for $85. Great deal. You can use Toyota service manual procedure to test pump wiring for ground. Let me know if you need procedure for ECU purchase site.
     
    #4 Stephen J Nesbitt, Dec 15, 2019
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