How To Remove Coolant Flow Control Valve 3-Way Toyota Prius Gen II 2004-2009 | CEL Error Code P1121

In this video, young mechanic Aiman will show you how to remove the 3-Way Coolant Flow Control Valve on a 2009 Toyota Prius I4 1.5L Hybrid Synergy Drive Gen II, which is the same as other 2nd generation model year (s) 2004, 2005, 2006, 2007 & 2008.

The second generation Prius, model years 2004-2009, uses a 3-way valve to control coolant flow between the engine, the hot coolant storage tank (thermos), and the heater core. Thus it’s involved in heating the passenger cabin (when requested), as well as reducing cold start emissions (with the coolant storage system). Anything that has to do with emissions illuminates the CEL Error Code “check engine” light; if something goes wrong with this valve, the “check engine” light comes on.

The valve is prone to sticking, and Toyota has issued a technical service bulletin (TSB) on this problem: EG001-08 M.I.L. “ON” DTC P1121. Valve replacement is recommended when the tree way CFCV failed.

The fix is replacing the valve. It’s mounted along the driver’s side frame of the engine compartment, near the radiator, and can be removed several ways. The first method is by elevating the hybrid inverter-converter unit and pulling the valve out from the top. The second method is by removing the driver side headlight and removing it from there. And the 3rd way is to remove the radiator top panel cover and pushing the radiator forward. In this video Aiman showed you all 3 methods above.

In theory, it should be fairly easy to remove and replace, but as you can see in this video, it could be quite involved. There are several specialized tools which may be required such as Hose Pinch Clamp (By Pittsburgh Automotive from HFT Harbor Freight Tools), hose clamp pliers, flexible hose pliers, fluid line clamp set and a few others. If you lose too much coolant, you may have to re-bleed the cooling system, which is tedious and time consuming. We also broke the bracket bolt which requires creative solution, something that happens from time to time with DIY repair.

If you need to replace the valve, in Part 2, Aiman will show you how to install it, here's the link:    • How To Install & Replace 3-Way Coolan...  

But if you're not comfortable doing it yourself, it should not be too expensive to have a local auto repair shop or garage do it for you. The part is not too expensive, especially if it's aftermarket. The labor is about 1.75 hours. Even a Toyota dealership might not be too bad for this type of repair.

Genuine OEM Part from Toyota Valve Assy, Water, P/N 16670-21010 is between $75-$100.

What is a Water Valve Sensor? Inside the water valve is a water valve sensor, which is a small electronic device that communicates with the ECM about the position of the water valve. It controls the coolant flow from radiator to Heat Storage Tank (CHRS) to auxiliary water pump, to the heater core, to the engine block and then back to the radiator, although the flow is primarily driven by main or regular electric water pump. This is called ICE (Internal Combustion Engine Cooling System, not to be confused with the hybrid cooling system, which is separate and has a separate pump.

Why Do Water Valve Sensors Fail?
The most common reason a water valve in a Prius fails is a malfunctioning radiator. When your Prius has a radiator that isn’t working properly, your engine overheats and wears down the sensor, eventually leading to a shorted water valve sensor circuit. Certain 2004-2009 Prius models are prone to water valve sensor failure, which leads to a sticking water valve.

A sticking water valve causes a disruption in the flow of coolant and can result in serious problems like an overheated engine or a coolant leak.

The Most Common Symptoms of a Failing Water Valve Sensor
The biggest symptom is an illuminated “check engine” light, but it could mean anything. The following symptoms are better indicators that something’s wrong with your water valve sensor.

Rough idle
Reduced engine power
A non-responsive throttle
The engine making a thumping or ticking sound
The hood feeling hot to the touch
The engine smelling “hot”
A coolant leak
Low coolant levels with no signs of a leak
The car not starting properly

How to Diagnose a Failing Water Valve Sensor
If you’re experiencing some of the symptoms of a failing water valve sensor, then we suggest using an OBDII code reader to confirm that your water valve sensor is failing. The OBDII code to look out for is P1121, which means that your water valve is stuck or your water valve sensor circuit is either shorted or corroded.

If you’ve confirmed that you’re dealing with a failing water valve sensor, the only way you can fix this issue is to replace the water valve.

Recording Date: November 26, 2018
Video URL:    • How To Remove Coolant Flow Control Va...