P1121

Been getting the check engine light intermittently, brought to Pep Boys where I failed inspection because of the P1121 code, Pep boys did not want to do the repair because the code was not specific but Toyota can break it down. I go to the dealer and they said coolant valve and fixed it for free, I am waaaay out of warranty, my Prius II is nearly 9 years old but the Toyota service rep said it's covered under some emissions technicality and waived the $125 diagnostics fee as well- who am I to ask questions.

 

Good think you are in a CARB state that has adopted the longer Emissions/Battery Warranty. Washington State is worthless-CARB: CARB emission standard adoption, but not the longer warranty of 10years/150K miles. All those folks are stuck with the shorter 8years/100K miles.

Actually, the valve isn't listed as a covered component under the Hybrid/Emissions components. But b/c it can effect emissions the service writer/tech probably made a push. Toyota probably realized it should have been listed, but won't say outright. Instead, will cover as customers come in and dealers ask for it to be warranty.

My 3-way coolant control valve was also covered under warranty. Jan 2014 @ 121,454 miles.

 

I too have the same p1121 code I'm wondering if it also has any connection with a humming-train-like sound from where the control valve is located when engine is running. It almost sounds like a "buzzzzzzz-buzzz-buzz buzz-buzzzzzzzzzzz". Thanks and I hate describing the sound like this but it is what it is, lol.

 

Some 3-way coolant control valves fail with that constant noise; the valve is trying to get into the right position, thus the constant noise. IF the valve should get into the correct position, the noise stops and CEL turns off; DTC P1121 is still logged, even though light is off. The valve motor could also burn out and simply get stuck in whatever position, and not make any noise.

If the engine cooling loops was worked on (drain/fill, replacement of a cooling component: water pump, thermostat), insufficient coolant in the engine loop might be causing the error, b/c of air. A leak could also cause a drop in coolant level, and contribute to the noise, b/c the coolant may act as a lubricant for the valve as it moves. Check the coolant level inside the radiator, after the car has sat overnight. IF the level is correct, then you most likely have a bad 3-way valve. Best to replace w/ an OEM valve. Others have replaced w/ aftermarket, only to experience the knock-off part failing a short time later.

If you wish to DIY, READ in its entirety to see if this is something you believe you can manage.
P1121 - Coolant Control Valve Replacement (with pics) | PriusChat