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P1121 - Coolant Control Valve Replacement (with pics)

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by Stomper88, Jan 24, 2012.

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  1. Stomper88

    Stomper88 Junior Member

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    Hello, I just replaced my Coolant Control Valve in order to address the Check Engine Light P1121. When I first got the CEL P1121, I scanned these forums and after some time (hours), I was able to figure out what was needed in order to replace this part. So, to save the next DIYer some research time, I will consolidate it into this post complete with, never before seen, photos of the elusive valve in its natural habitat.

    If you just got this code, you should first make sure your coolant is not low. Some people have reported their P1121 code going away permanently just by bringing the coolant level up to proper levels. For me, the code would come on and off on its own, even when the coolant level was correct.

    Part Number 16670-21010
    Time to replace (including ICE coolant drain and refill) - 4-6 hours (with breaks)
    Difficulty level - Intermediate (tougher than an oil change)
    Total Cost - $120 ($80 for part, $40 for 2 gallons of Toyota Super Long Life Coolant)
    Dealer Replace Cost - $400-$500

    Tools needed:
    Phillips screw driver (for various clips)
    Flat screw driver (for various clips)
    Pliers for hose clamps
    10mm and 12mm deep sockets for the valve mount

    Optional tools (makes it easier):
    Cable operated hose clamp pliers Link
    Spill Free Radiator Filler Kit ($20-$25 on amazon)

    Here is a video showing valve inside and outside of Prius.

    One poster mentioned that clamping the three hoses allows you to skip the draining and refilling of coolant. This might be a good idea if you have recently replaced the ICE coolant, but chances are this part is going to fail around the time that you should be swapping the coolant anyway. Here is his post in case you want to try it. Link.

    Procedure:

    1. Remove the radiator cover and under engine cover. Mark the upper hose connected to the valve. I used some floursecent paint. This is very important because once the valve is out, the two upper hoses will be difficult to differentiate.

    2. Drain the ICE coolant. There are many references on this forum on how to do it. This is my favorite post that covers it. Link. I just removed the engine under cover LH (Driver side), then reached over to the thermos (heat storage tank) and twisted the yellow valve until the fluid start pouring. The LH fender is shaped to drain the fluid out of a hole, so no need to remove the fender trim, too. I did not bother opening the radiator or engine coolant drains.

    Lets pause for some commentary on the valve. The three hoses attached to it are held on by spring clamps. The largest frustration for this job is trying to get the spring clamps off in the very tight space that you are given. If you are comfortable removing (or raising) the inverter, your life just got easy. Removing the inverter will not only give your pliers easy access to those two upper hose clamps, but it will also make removing the valve mounting bolts a piece of cake. But, the mounting bolts are not really that hard to reach with a tiny socket wrench and some deep sockets. Another option for the hose clamps is to buy cable operated hose clamp pliers. I discovered these after I was finished and would have easily paid the $40 for them. It took me a total of about an hour of to get the three clamps off and back on due to the tight space. With the inverter out of the way, or the cable pliers, I bet I could have reduced that to 5 minutes. These two options are optional. I am just an average DIY and I was able to do it without them, but I would have fell in love with (or at least stared longingly at) any woman that walked in with a pair of those cable pliers when I realized my normal wrenches were too big to reach the clamps, and my coolant was already drained out.

    3. Remove the power connector from the valve, then move the coolant drain pan under the valve and remove the three hoses attached to the valve.

    4. Now remove the two mounting bolts holding the valve.

    5. Remove the valve from the engine compartment. I could only do this by slowly wiggling it downward and out from below (safety goggles will prevent coolant and dirt from falling in your eyes during this). The inverter blocks removal from above.

    6. Now attach the two bolts on the new valve and reattach the three hoses and the power connector.

    7. Refill the coolant per the procedures in any of the coolant posts. This is the most time consuming process (took me 2 to 3 hours). Do not forget about the bleed valve on the right side of the radiator. There is a big yellow sticker pointing to it and it takes a 6mm hex wrench. I used the paper clip method that Patrick Wong describes to make the heat storage pump run for 15 seconds at a time.

    Hope this helps the next P1121 victim. ;)

    Attached Pictures:
    The first picture shows the valve in yellow, the upper hose in green, and the middle hose in blue.

    The last picture shows the old and new valve close enough to see what I suspect is the failure. In the old valve, you can clearly see the valve is stuck halfway between open and closed.

    Attached Files:

    frodoz737, tnana, HaroldW and 11 others like this.
  2. Stomper88

    Stomper88 Junior Member

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  3. 2009Prius

    2009Prius A Wimpy DIYer

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    Nice write up and video too! What camera were you using to take the video with?
  4. Stomper88

    Stomper88 Junior Member

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    Thanks. I used a Canon SD1300 IS.
  5. northwichita

    northwichita .

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    This is part no. 16670-21010 ?
    Also does the back cover of the valve come off, I saw the screws, the inside would also be interesting to see.

    .
  6. Stomper88

    Stomper88 Junior Member

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    I updated my post with the part number, you are correct.

    I am attaching a picture of the internals. I was able to manually rotate the valve, which is attached to the big white gear with teeth hiding under the white plastic plate. It appears that a simple motor is behind the silver plate and spins the various visible gears to rotate the plastic valve.

    Attached Files:

    2 people like this.
  7. 2009Prius

    2009Prius A Wimpy DIYer

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    So were you able to determine which part inside failed?
  8. Stomper88

    Stomper88 Junior Member

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    No. The valve turns, but its stiff, not sure if its too stiff. Also, the motor could have gone out. The only other thing is the position sensor (with the three wires) might have failed. Nothing visible to indicate what failed.
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  9. lessismore

    lessismore New Member

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    I found the valve for $53 plus $10 S&H online at olathetoyota. And thanks Stomper88 for the great step by step instructions!
  10. philmcneal

    philmcneal Taxi!

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    what is the probability factor of this part failing on me? did anyone replace this part out of preventative maintainence?
  11. Stomper88

    Stomper88 Junior Member

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    If you are planning to do a drain and refill for normal maintenance and you are in the model years that have the TSB on this (I think 2004 and 2005), you might want to consider replacing it at the same time since you can order it for pretty cheap. Otherwise, if might fail right after you put fresh coolant in.

    If you do not have the coolant replacement due, then I see no reason to replace it. It is not a critical part (if it fails, you can keep driving with no risk). It wont leave you stranded. I made several 1000 mile road trips after the light came on and never had any issues.
  12. philmcneal

    philmcneal Taxi!

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    ^^

    HI STOMPER thanks for the quick reply!

    I plan to do a big service at the dealer! this includes the TSB for the new inverter pump coolant, replacing the engine water pump at my cost because it is leaking (300 plus tax), a drain and fill of the transaxle fluid, and an oil change. Since my coolants are being replaced I'll bite the bullet and get this piece fixed too since my prius is at high mileage (244000 km) and don't want no bs since I use my car a lot!

    See if I can negoiate with the dealer since I'm doing a big service hehe thanks stomper!
  13. philmcneal

    philmcneal Taxi!

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    Man im so sad the part is goign to cost me 199.99 alone... it has a 55% markup (89 bucks profit?) wonder if its cheaper for us canadians to order from the states and ship it over here T_T
  14. lessismore

    lessismore New Member

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    I just replaced mine and would never replace it unless the valve actually fails and throws the code. I bought the cable operated hose clamp tool and it was worth every penny of the $40 cost from Sears. I also found it easier to pull the vertical hose off after I pulled the valve. I pulled the other end of the vertical hose off the coolant tank then reattached the hose to the valve before installation so I wouldnt have the fun of trying it after it was in place. Took me about 4 hours.
  15. maverick1970

    maverick1970 New Member

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    Mr. Stomper you are outstanding!!! Thank you so much for the post. I have read this and have hope :) I'll explain.

    I got in my car yesterday afternoon to go home from work, and boom the check engine light came on. It was too late to get it checked out so I went first thing this morning to the stealership. First they wanted $79.95 just to check the code. I was told it would apply towards the repair if something was found wrong. Ok I said...

    Well they took it back while I waited in the waiting area drinking a couple cups of coffee watching the Today Show blah...blah... and a half an hour later, the guy who checked me in comes and gets me. We walk back out to the service check-in area and he tells me about the codes, how the coolant flow control valve is in a stuck state, and that it will cost $568 to repair (parts & labor). I wasn't happy about it by now means. He said he would need to order the part as they didn't have one in stock nor did any of the other dealers in metro Atlanta. I said ok order the part which was $87.03 after taxes. After ordering the part, I had to get my butt to work, so I left and went straight there.

    I got to the office and talked my situation over with some of the guys. My boss suggested that I check the forums to see if I could find out what other people have done. I didn't have time to do the research at work, so I was bummed out all day until about 20 minutes ago when I found your post.

    That's why I have hope dude. I popped my hood, took the plastic cover off and BAM... I can see the valve right away. Seems straight forward. I've got deep sockets and extension... so it doesn't seem like a big deal. I'm definitely going to pick me up some of those cable operated hose clamps. I've flushed my coolant system on my Ford Ranger and HATE taking those things off. So yeah I can definitely see the value in having those. I off all next week so looks like I've got at least one day planned :)

    Let me buy you lunch!! Seriously, PM me.

    Stay tuned...
    maverick1970
    aka Jeremy ;-)
  16. maverick1970

    maverick1970 New Member

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    Oh I forgot, I had a question... did your check engine light clear on its own after you replaced the valve?
  17. Patrick Wong

    Patrick Wong DIY Enthusiast

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    DTC P1121 is logged by the engine ECU. Any engine ECU codes can be cleared by disconnecting the 12V battery negative cable (easiest where it attaches to the body) for a few minutes. This allows the engine ECU memory to be powered down, and that will clear the check engine light.
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  18. Stomper88

    Stomper88 Junior Member

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    I used an ELM327 with my android tablet to delete the stored code (which removed the check engine light), but Patrick's method sounds easier.

    Good luck and feel free to ask any questions. When I think back on it, the most annoying part was the refill. I remember someone mentioning a device that can help make that faster. I think it fit on the refill spout and pressurized it. It should be in several of the coolant drain/refill posts.

    No need for lunch, just knowing that my posts are helping others is reward enough. I love the feeling of contributing to something positive.
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  19. maverick1970

    maverick1970 New Member

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    If I clear my ECU of error codes, shouldn't the code reappear if my coolant control valve is truley stuck?
  20. Stomper88

    Stomper88 Junior Member

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    Yes, after clearing the code, mine would usually take a few days to reappear. I think a drive longer than 20 minutes would trigger the code.

    In fact, if you do nothing, it will probably turn off on its own and then come back on sometime later. I think it depends largely on your driving style. I drive mostly short 10-15 min drives. So it sometimes cleared itself. Then it would return on a longer drive.
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