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Heater Core Pump Rapid Cycling

Discussion in 'Gen 2 Prius Technical Discussion' started by tkeenan, Dec 24, 2012.

  1. tkeenan

    tkeenan New Member

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    Vehicle:
    2005 Prius
    Model:
    Three
    The heater core pump is acting up on my 2005. It cycles rapidly on-off-on-off at a rate of about 2 cycles per second. I haven't seen this discussed here, so hopefully I'm not bringing up an old topic.

    It appears that the pump may be cycling due to perhaps a stuck switch someplace. Recently, the defroster has become less effective at clearing the windshield, and heat seems to be not as strong or consistent as it once was.

    Is there an overspeed switch on the pump? (might be cycling because of no load / air in the system?)
    This would not seem to be an issue because the cooling system has never been opened or drained.

    Is there an overpressure switch on the pump? (main pressure switch defective, and overpressure switch is causing the pump to cycle on/off) This would not seem to be an issue because I doubt that a water circulation pump would have a pressure limiter.

    Is there a temperature switch someplace that turns the pump on/off based on water temperature? (perhaps the temp switch is stuck in 'already hot' mode?)

    Where are the switches/relays associated with the heater core pump located?

    Thanks in advance!

    Tom
     
    #1 tkeenan, Dec 24, 2012
  2. nh7o

    nh7o Off grid since 1980

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    To your questions: No, no, and no.

    The circuit is very simple. From the Hybrid Control ECU, there is a line WP that operates the relay A/C WP. When WP goes to 0V, the relay is closed, and the pump runs.

    The pump runs when the engine is off to maintain heat in the core. First thing is to go into the main engine room fuse/relay block, find the A/C WP relay, and listen if it is cycling on and off the same as the water pump. If so, then the control signal from the ECU is suspect. If not, and the pump is getting a stable voltage, then the pump has a problem, likely something to do with the brushes.
     
    #2 nh7o, Dec 24, 2012
  3. Brian Thompson

    Brian Thompson New Member

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    #3 Brian Thompson, Jan 5, 2013
  4. Brian Thompson

    Brian Thompson New Member

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    Hi Tom,

    My 2004 has the same symptoms, low heat, defroster is not as effective. Have you found out anything since the reply that was posted to your original question?

    Thanks
     
    #4 Brian Thompson, Jan 5, 2013
  5. tkeenan

    tkeenan New Member

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    I have not yet discovered anything significant. It looks like I will need to dismantle a portion of the engine compartment just to get at the pump, so the investigation is currently on hold.
     
    #5 tkeenan, Feb 6, 2013
  6. Racbca

    Racbca Junior Member

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    Location:
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    Vehicle:
    2005 Prius
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    ----USA----
    I believed I am having the same issue starting around 95k miles and it it now 110K miles. I am not able to attached the sound recording I made. How do I attach a .wav file? The sound is coming from the firewall driver side.
     
    #6 Racbca, Apr 13, 2013
  7. nh7o

    nh7o Off grid since 1980

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    I think you need to have 5 posts to be able to send attachments. The House of Pancakes forum is for the purpose of practice and testing.
     
    #7 nh7o, Apr 13, 2013
  8. Racbca

    Racbca Junior Member

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    Thanks for the information. I can attach pdf, txt, and pictures.

     
    #8 Racbca, Apr 13, 2013
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