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    jmacrae New Member

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    I had my hybrid water pump replaced (free, under recall) about a month ago. Now the check engine light comes on intermittently, and it's with error code 1121 (Coolant flow control valve sensor stuck). I've seen other people on this forum hypothesize that the work could cause this error (if not bled properly, leaving air in the system). But my dealer said the work had nothing to do with this error and I need to replace the control valve ($100 part and $400 labor). Any ideas on how to suggest to my dealer that it could, in fact, be due to their work and that I think they should fix it for free?
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    seilerts Battery Curmudgeon

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    No, it has nothing to do with the work that your dealer did.

    Now, did they do the engine water pump? Have you ever had it done? They are highly prone to failure, and it is possible to get that code when the system is low on coolant due to the slow leak out the weep hole.
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    jdenenberg EE Professor

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    Air in the Engine coolant system or low engine coolant level can cause 1121 as the coolant acts as a lubricant foe that valve. Top off the coolant first and see if the problem goes away. It did for me and has not come back in 120k miles.

    JeffD
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    jmacrae New Member

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    Are there two different water pumps, or is the "hybrid water pump" the same as the "engine water pump"?
    I was told that the service (replacing the hybrid water pump) did involve bleeding the coolant - is that not so? And if it is so, then shouldn't the dealer have put enough coolant in after flushing the system when they replaced the water pump?
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    jdenenberg EE Professor

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    There are several coolant pumps (actually 4) in a Gen2 Prius. The two main ones are the engine coolant pump which is a standard mechanical pump (in a Gen2) which is driven by the serpentine belt and the other is an electric coolant pump that provides cooling to the Power electronics (Inverter) and the Hybrid Synergy Drive (Tranny and two motor-generators).

    When either of the two independent main cooling loops is drained and refilled, care must be taken to get all of the air out of the system. This is a tedious, time consuming process and not all technicians will do a complete enough job.

    JeffD
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    seilerts Battery Curmudgeon

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    The inverter has a separate loop in the radiator. The engine coolant is completely separate. Now, I suppose it is possible that the tech pulled the wrong hose and drained part of the engine coolant, which is now causing the problem. Regardless, check your coolant level, and the weep hole in the engine water pump.
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    jmacrae New Member

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    Thanks, I'll check the coolant level tomorrow. Where will I find the weep hole and what am I looking for when I check that?
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    jmacrae New Member

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    OK, so I checked and the coolant level is almost completely empty!!! I guess that could definitely be the problem. I'll go get some Toyota juice tomorrow. So, not to sound like an idiot, but just to be sure I understand this correctly - the hybrid electric water pump runs a cooling system that is *completely independent* of the ICE coolant system, which is the system I just checked. So that would explain why the dealer said that even though the cooling system was flushed, it has nothing to do with this problem. Have I got it?
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    seilerts Battery Curmudgeon

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    Yes, that's it.

    To look for the leak in your ICE water pump, check the pulley, and the top of the A/C compressor. If you see pink bird turds, then it is bad, and you are looking at a $350-$450 repair.
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    jmacrae New Member

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    OK, thanks. So I thought I would just unscrew the cap on the translucent white box (reservoir?) and pour the pink juice (Super Long Life coolant fluid) in until it reached the top line. Then I read something here about taking off the radiator cap and running the engine and it's sounding much more involved. If all I need to do is fill it up, can I just fill up that reservoir box and be done?
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    jdenenberg EE Professor

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    You can fill the plastic coolant overflow reservoir, but then after an engine heat up - cool down cycle you may have to put in some more coolant as some will stay in the ICE coolant loop. After doing this a few times the level should stabilize.

    Make sure you get Toyota Super Long Life coolant (the pink stuff, not the older red concentrated Long Life coolant). It is premixed to 50% concentration so don't add any water.

    JeffD
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    Patrick Wong DIY Enthusiast

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    If the reservoir mounted on the radiator is empty, who knows how full the radiator itself is?

    This is why you must remove the large black plastic panel over the radiator for access to the radiator cap, so that you can see how much fluid the radiator needs and fill to the neck opening.

    Suppose the radiator fluid is down several inches. It will take a very long time for the radiator to be filled via the reservoir, and this will depend upon you noticing the reservoir needs to be replenished repeatedly, several heating and cooling cycles, etc etc. In the meantime you may damage the engine due to continued operation with insufficient coolant.

    The purpose of running the engine while filling the radiator is to get air out of the system, where the coolant level is significantly low. That is not necessary if you find that the fluid level in the radiator is reasonably high.
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    jmacrae New Member

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    Well, the reservoir wasn't completely empty, so two cups of coolant filled it up and it hasn't gone down. That was last week. Now, yesterday, the check engine light came on again, so I decided to bite the bullet and just go have Toyota replace the valve/sensor. (I was, however, get them to reduce the fee from 3.5h labor to 2.1h when I brought in the TSB that showed the estimated 2.1h labor, so it only cost me $310 plus the remainder of the $21 jug of coolant). I noticed, however, when I drove it home, that after I turned it off the motor that pumps the coolant into the thermos is much louder than it used to be. I'll bring it back to have them check it, but does anyone have an idea why that might be?
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    Patrick Wong DIY Enthusiast

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    1. Could it be that you are just paying more attention to the car now, and the same noise appears louder than in the past?

    2. If the noise is actually louder, then there may be air in the cooling system.
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    jmacrae New Member

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    No, the noise is definitely louder than it ever was before. Sounds almost like a toilet flushing every time I turn off the engine. And I do hear air gurgling by as well as fluid sounds. I took it back to have them check & make sure it was OK, and they said "there isn't any way to bleed the system, but I (the mechanic) let it drain for 3 hrs". He said that the coolant level in the radiator was fine, and so not to worry about it. It's just weird, hearing a toilet flush every time I turn the car off.


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    seilerts Battery Curmudgeon

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    If you hear it gurgling, then there is air in the system. Bleeding it is not easy.

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