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2008 Toyota Prius - Coolant Control Valve

I replaced my coolant control value about 2 yrs ago after light/ code came on, about a month later light/code came back on, I replaced it again thinking I had put in a faulty one. I got about a yr and the light/code came back, I replaced it again. Now about 9 months later the light/code is back. Something must be causing the control value to go bad, anybody have this problem? Any suggestions? HELP…

What is the code in Pxxxx form, where xxxx is for 4 digits?



In 2 years the OP is getting ready to replace this valve for the 4th time.
Replacing the valve is apparently not the cure.

Well, @KevinMerrigan did not tell us what the code is, it may be not even P1121 at all

For p1121, the most likely possibilities are

  • faulty valve
  • crud in cooling system eventually clogs replacement valve
  • faulty tank outlet temperature sensor
  • faulty water pump or relay
  • faulty ecm
  • faulty wiring harness

My guess is the cooling system is rust & debris-clogged and it needs a thorough flushing and refill w/ fresh Toyota approved coolant.

Yes, the code is P1121. That has been the code every time. Sorry, should have said that.

That’s my guess too.

Toyota original fluid is good for 10 years and 120K miles, but if it was replaced by any other (or “universal”) coolant, all bets would be off.

I have 2005 Prius where the electric pump was replaced under recall somewhere around 2010 and with mileage around 50K, system was flushed. I’m still on original control valve at 120K miles at moment, and the coolant looks as good as new.

Thank you for all the responses. I will flush the cooling system this weekend and hope that my problem is solved.

You still have the factory fill in the cooling system? The inverter coolant also should have been drained and filled at 10 years/100,000 miles.

BTW, I have never drained rusty coolant from an aluminum engine.

make sure to use Toyota specific (red) fluid

also, the process is quite involved form what I recall, as you also have to drain/fill the heat retention tank and to properly do all of this it is a special procedure, it involves manipulating the valve under question

This is the first I heard of thermos technology used in car engines. It seems like a pretty good idea to reduce emissions. Is it used in any car other than the Prius?

AFAIK, even Prius abandoned this technology and transitioned to the coolant loop in the diverted segment of the exhaust pipe.
The trouble of the heat retention tank is two-fold: it takes a lot of coolant to store heat AND it make the tank to sit quite low in the left/front bumper area, so it may be damaged with hitting a high curb or parking lot stopper.

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