Newbie got questions about P1121

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ramthecowy, May 8, 2021.

  1. ramthecowy

    ramthecowy New Member

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    Hello all! So I realize this question gets asked a lot, so apologies. In this case it's a 2008 Prius that's throwing a P1121 code intermittently, it weirdly works better in colder temps over the winter than in the spring/summer warmer days. What I hear is (if I'm not wrong) the engine coolant heat recovery system pump running - sometimes it doesn't run at all, and sometimes it runs for just a second before abruptly stopping, sometimes it works perfectly. If my understanding is right, that pump failing should throw a P2601 code, not a P1121, so does that mean the valve is still the component at fault? I'm not sure of the logic of the system and what exactly the interaction is between the valve and the pumps.
    I checked coolant levels (ICE okay, topped up inverter) and as far as I know there are no leaks otherwise I would have already realized. Temps on drives seem to be under control (I've never seen higher than 91C, usually warms up and stays in the 80-90C region). So I don't think this is the issue.
    Any advice appreciated, thank you!
     
    #1 ramthecowy, May 8, 2021
  2. JC91006

    JC91006 Senior Member

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    p1121 is a bad 3 way coolant valve. It won't affect the car's drivability if you don't fix it. Your check engine light will remain on if the fault is present.
     
    #2 JC91006, May 8, 2021
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  3. ramthecowy

    ramthecowy New Member

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    Interesting! So there must be some communication between the valves state and the pumps then. Neat, thank you
     
    #3 ramthecowy, May 10, 2021
  4. JC91006

    JC91006 Senior Member

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    This is an emissions related part. In CA, this part is covered for 10 or 15 years, 150k miles. Whichever comes first. I had my 2008 Prius come up with a fault within the 10 years and got a free replacement under warranty
     
    #4 JC91006, May 11, 2021
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  5. mr_guy_mann

    mr_guy_mann Senior Member

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    Coolant temperature from various sensors in different parts of the system, 3-way valve position feedback, ICE operational state, power mode (Ready, "on", accesory, "off") - all of these are inputs to the engine ecu. Based on its programming it will activate outputs such as the 3-way valve motor, or the storage tank pump.

    That's all that any ecu will do- inputs, processing (whatever it is programmed to do), and outputs.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, May 11, 2021
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  6. ramthecowy

    ramthecowy New Member

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    Follow up question since I've started hearing this sound a lot more (mp3 attached inside zip). It's mainly noticeable during stops when the ICE isn't running.
    I've looked online and found one video ("How To Quickly Check Your Prius Inverter Water Pump" by Hometown Hybrids) that points at the inverter pump which is scary...
    ...while some threads on PriusChat ("Inverter pump?" by member HiccaBurp in gen 2 forums) say its the 3 way coolant valve which I do know is on its way out in my car given that it runs randomly and the P1141 code appears occasionally.
    I would appreciate any light that can be thrown on this!
     

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    #6 ramthecowy, Sep 16, 2021
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