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DTC P1121 2004 Prius @96k

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by labumm, Jul 23, 2011.

  1. labumm

    labumm Junior Member

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    Vehicle:
    2010 Prius
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    II
    The narative:
    The check engine light came on and the DTC reads P1121, which indicated trouble with the coolant control valve. I cleared the code several times and it reappeared. It has been >100F every day here in OK. Investigating under the hood I noticed the engine coolant overflow tank was empty. Opening the radiator cap showed no visible coolant in the tube! OK, I have not seen any leaks and the car has had dealer service 3K ago. I filled the radiator and overflow w/ SLLC (Toyota pink). The DTC has not reappeard and it has been about a week.

    My comments/questions:
    1) the car is getting old and I can accept a little maintanance.

    2) I can understand why low collant/air in the lines might cause a false P1121.

    3) I am confused why there was no warning of low coolant.
     
    #1 labumm, Jul 23, 2011
  2. seilerts

    seilerts Battery Curmudgeon

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    Well, either the engine will overheat, and drop a red triangle but NOT set a code; or, you get P1121, when the coolant is low.

    You probably have a leaky engine water pump. It will leak coolant past the seal over thousands, if not tens of thousands of miles, and never leave a noticeable puddle. The only clue might be a few pink crusty spots underneath the pump pulley. The pump has been redesigned and should last the life of the car now.
     
    #2 seilerts, Jul 23, 2011
  3. labumm

    labumm Junior Member

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    Good to know.

    But is there really no coolant level sensor? That suprises me given the appearent complexity of the system.



     
    #3 labumm, Jul 23, 2011
  4. seilerts

    seilerts Battery Curmudgeon

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    Right, there is no coolant level sensor. The real mind-boggling one is that you can get the red triangle when the engine overheats, but upon being towed to the dealer, there are no diagnostic codes to be found.

    The engine water pump is not a terribly hard DIY job, but it is worth reviewing some of the stories here for tips on getting the coolant thermos refilled if you choose to drain it in the process.
     
    #4 seilerts, Jul 23, 2011
  5. Vct

    Vct New Member

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    Four
    +1. Hot summer = low coolant. Had the same problem. Filled up the engine coolant and the CEL P1121 vanished. Occasionally comes on every now and then but does not bother me anymore.
     
    #5 Vct, Oct 19, 2011
  6. seilerts

    seilerts Battery Curmudgeon

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    Not true in a closed system. The level will vary evenly between full hot and full cold, unless there is a leak or you have blown head gasket. Check your engine water pump.
     
    #6 seilerts, Oct 19, 2011
    1 person likes this.
  7. Vct

    Vct New Member

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    I finally bit the bullet and got the valve replaced. Dealer/$stealer wanted $550. I bought the part valve for $75 and had a locl mechanic replace it for $100 labor.
     
    #7 Vct, Nov 27, 2012
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