P1121 error code help!

Discussion in 'Newbie Forum' started by Dylan Watson, Dec 31, 2020.

  1. Dylan Watson

    Dylan Watson Junior Member

    Joined:
    Apr 10, 2019
    6
    2
    0
    Location:
    Piqua
    Vehicle:
    2007 Prius
    Model:
    II
    Hello, I have a 2007 Prius with 132k miles and my dash light came on for check engine. it came back with a P1121 code. The dealership I took it too said my idler pulley needed replaced soon when I had my brakes serviced there a couple weeks ago. My question is, is there error code likely due to the idler pulley part? Or something else completely? They weren’t very helpful over the phone. Any help would be GREATLY appreciated! I haven’t noticed my car driving any different since the light has came on. No weird sounds or anything like that. I just want to be proactive about it before something does happen.
     

    Attached Files:

  2. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    13,895
    9,865
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Something else completely. It comes up fairly often here on PriusChat. You can do a search here to learn more about it.

    That's the way warning codes are supposed to work. Best case, you get them earlier than any problem you would notice in driving the car.
     
  3. John321

    John321 Senior Member

    Joined:
    Nov 16, 2018
    421
    551
    0
    Location:
    Kentucky
    Vehicle:
    2008 Prius
    Model:
    Two
    On a Prius Hybrid this would indicate a stuck or slow moving coolant valve. The coolant valve moves and if the position sensor feedback on the valve doesn't indicate the valve is in the position it should be the vehicle will show a code that indicated the valve position isn't where it should be.

    P1121 2007 TOYOTA PRIUS Coolant Flow Control Valve Position Sensor Circuit Stuck (With Video)

    Did you change the coolant recently? It is not unusual for this valve to fail after a coolant change, it happened to me and I ended up buying a replacement valve and replacing this valve. If you are lucky the fault will reset and the valve won't stick again. You would need Techstream to reset fault.


    another video : there are many on you tube if you search Toyota Prius 3 way cooling valve- a very common failure point

     
    #3 John321, Dec 31, 2020
    Last edited: Dec 31, 2020
  4. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    13,895
    9,865
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Or, it indicates that the valve isn't stuck or slow moving, but its position sensor does not report its position accurately.

    As is always the case with a trouble code, one has to think about the detection condition—what the car's computer has to see to set this code—and the limits on what the computer is able to see. In this case, the computer is saying "hey, I told this valve to move to position X, but the signal coming back from the position sensor doesn't say it's at X." Naturally, the reason for that could be anything from the valve being mechanically stuck or slow, to the position sensor, to the wiring between the computer and the valve and sensor. (In super rare cases it could be a problem with the computer itself.)

    Those are the possibilities it's always necessary for the human to go through, process of elimination, because the computer itself doesn't know which of those is the real cause.

    As it happens, potentiometers used as position sensors in the Prius contribute to a number of familiar problems, so it's not unlikely to be at the bottom of a P1121.

    [​IMG]
     
Loading...