Engine Code P1121 with check engine light

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Rick 432, Nov 25, 2025 at 3:01 PM.

  1. Rick 432

    Rick 432 Member

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    I have a 07 Prius that just displayed check engine light. Code found was P1121 which is a coolant flow malfunction according to research I did. Checked coolant for inverter and it is moving very nicely. Inverter is very hot! Information I found says it is a coolant inverter valve. Also, prior to this issue when I stopped the car the sound from the engine (pump antifreeze/coolant into storage tank) was odd. Snapping sounds and not the usual buzzing sound. Anyone every change one of these flow valves? Thanks guys.
     
    #1 Rick 432, Nov 25, 2025 at 3:01 PM
  2. ChapmanF

    ChapmanF Senior Member

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    #2 ChapmanF, Nov 25, 2025 at 3:30 PM
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  3. PriusCamper

    PriusCamper Senior Member

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    While I may agree checking the inverter cooling system isn't perfect, it also isn't that far off when you're new to it all... Why not just tell OP that the sensor in the 3-way coolant valve has gone bad and it happens in almost every really old gen2 Prius and it's fairly easy to replace and there's lots of cheap after market ones that runs just as good as OEM: http://www.ebay.com/itm/394097566363 And you might also help OP by letting them know they can go years without fixing this problem and it won't be any concern other than a slight loss in MPG when engine is running cold.
     
    #3 PriusCamper, Nov 25, 2025 at 4:17 PM
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  4. Rick 432

    Rick 432 Member

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    Just looking at threads and what is on the internet. Having written that, my inverter was hot after I drove the car today. Maybe I have multiple issues. I will look at that coolant control valve. I have never replaced one of those so I will see what happens. Thanks for the information.
     
    #4 Rick 432, Nov 25, 2025 at 6:17 PM
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  5. Rick 432

    Rick 432 Member

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    Thanks so much for the information. I appreciate the impute
     
    #5 Rick 432, Nov 25, 2025 at 10:49 PM
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  6. nolotank

    nolotank Junior Member

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    As others have mentioned, P1121 is for the 3-way coolant control valve which is part of the engine coolant loop, not the inverter coolant loop.

    Many on these forums, myself included, have been burned by aftermarket or knockoff valves. For this part (Toyota 16670-21010) I would strongly recommend going OEM.

    Also curious how you assessed that the inverter was hot, I believe it's normal for the cover and coolant reservoir to be warm/hot after a drive. If you had a serious inverter overheating problem, I would expect a red triangle on the dash with P0A93.
     
    #6 nolotank, Nov 27, 2025 at 5:54 PM
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