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P1121 PSA - Low Inverter Coolant

Discussion in 'Gen 2 Prius Main Forum' started by Josh Gold, Dec 28, 2022.

  1. Josh Gold

    Josh Gold Junior Member

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    This is just a public service announcement for any rookies like me. I got the P1121 code and ordered the part to replace my coolant flow valve. I did not even look at the reservoir for the inverter coolant initially because I heard they were totally separate cooling systems, but when I lifted the hood to install the part, I noticed that reservoir was below Low.

    So, I added SLLC, bled it to get rid of any air pockets, cleared the code, and it hasn't shown up yet.

    So it seems P1121 can indicate low flow on the inverter side of the cooling system, and not just a bad coolant flow valve.
     
    Prius Rising likes this.
  2. ChapmanF

    ChapmanF Senior Member

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    No, P1121 is absolutely specific to the coolant control valve, in the engine cooling system, and the two systems are completely separate. The code has nothing to do with the inverter cooling system.

    It is good that you noticed the separate issue of the inverter cooling system being low, and topped that off.

    You have cleared your P1121 code, which was set at a moment when the engine coolant valve position sensor reading didn't change as the ECM tried to move the valve, or the thermos outlet temperature didn't change the way it should have based on the valve position. The code will stay clear until one of those things happens again.
     
  3. Josh Gold

    Josh Gold Junior Member

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    Thank you for the correction, sir! I will be replacing the coolant valve and burping the system this weekend!
     
    bisco likes this.
  4. Josh Gold

    Josh Gold Junior Member

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    An update on my own experience replacing my coolant valve (so far). I finally had a warm, sunny day outside, so I went about replacing the valve. I mostly followed the tutorials from this smart kid on Youtube:

    Part 1 - Removing the Coolant Valve
    Part 2 - Installing the new Coolant Valve
    Part 3 - Burping the System

    I also took some tips from this post. The one thing I did not fully consider was the amount of fluid in the tank and how difficult it would be to clamp off the hoses. Even after clearing space, it was still pretty tight. In retrospect, I would have removed the lower splash guard, as well as at least part of the fender, enough to get the headlight out, before I even started. Once I did that, it gave me more room, but it was still difficult to get to the lines and clamp them with the long nose locking pliers I was using.

    Ultimately, I ended up losing a lot of the coolant from the CHRS tank while trying to get the 3 lines un-clamped from the valve and getting the new one on. So, following the burping video about jumping the connection, I did that a few times, and then took the car on a test run. It drove fine, until I increased the temp and the fan, which others had said to use to exercise the CHRS. That caused the red triangle of death and the temp warning light. So I backed it off, and re-attempted the burping process until I saw coolant flowing back up into the funnel. I took another test drive and all seemed good.

    The next day, I started up the car in the morning and received the P1151 error. I decided to keep driving and test it out. It was chilly, but I didn't really need the heat. Twice, I received the red triangle briefly and I could hear the swishing sound of liquid, which indicated to me that there was probably still air in my system, but as I was driving, I backed the fan and the temp all the way down and it no longer appeared. Once I got to my destination, I let the car cool down and then went through the burping process yet again. This time, no warning lights, no swishing/gurgling sounds.

    I'm hopeful that I've got everything back in working order.

    Lessons learned?

    * Clear as much space as you can to get to the hoses as best you can. Esp. the one on the bottom.
    * Clamp the hoses as tight as you can with a decent set of locking pliers/clamps. Mine were cheapies that didn't work well.
    * If you ended up losing coolant during the process, the burping process may take 2-3 tries to get all the air out.

    Would it have been easier to drain the entire tank and refill? Perhaps. I spent about 2 hours total unscrewing/bolting things to get to the valve, clamping hoses and backing off the metal clamps, replacing the valve, and putting it all back together. With my hands and driveway covered in the pink stuff. Plus I spent another hour or so in testing/burping the system.

    But I'm an amateur mechanic at best, so I'd call this another learning experience :)
     
  5. highmilesgarage

    highmilesgarage Active Member

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    bleeding the coolant is not that complicated in Toyotas specifically the Prius. IMO you can even do it without jumping the relay pump or set the car in maintenance mode. I just replaced my coolant heater valve too just last week. It just takes a while, last time I used vacuum to fill in coolant in the inverter which I think is around $30 in amazon. You need to have an air compressor to use this one and is really quick and no spillage (no Techstream or bi-directional scanner required).

    I forgot which brand I bought but it's similar to this..


    I used to have a Jaguar/Lincoln LS before that requires special bleeding operation (way too complicated) and that vacuum refill made it simple.
     
    #5 highmilesgarage, Mar 7, 2023
    Last edited: Mar 7, 2023
  6. qmanqman

    qmanqman Active Member

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    Got same code and replaced pump couple weeks ago