Prius P1121: Coolant Flow Control Valve Position Sensor Stuck

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). image Anything that has to do with emissions illuminates the “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 technicial service bulletin (TSB) on this problem: EG001-08 M.I.L. “ON” DTC P1121

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 by elevating the inverter and pulling the valve out from the top.  With good use of hose clamps, the job can be performed without loosing more than a spash of coolant.

Warranty time for valve replacement, as listed in the TSB, is 2.1 hours.  Luscious Garage charges 1.75 hours.

Labor, 1.75 hours: $210
Valve Assy, Water, P/N 16670-21010: $78.59
Qt Super Long Lift Coolant: $5

Total with tax: $301.53

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Any references to pricing of parts, labor, or estimates of any kind were accurate at time of publication. Please contact us for updated pricing.

7 thoughts on “Prius P1121: Coolant Flow Control Valve Position Sensor Stuck

  1. I have the Gen 2 Prius and have received the P2601 code two days in a row now right after I changed the thermostat.
    I changed the thermostat because the car was running cold and had gotten P1116 code a couple days in a row.
    Do my service codes have anything to do with the inverter or flow control valve?

  2. I am interested in buying 1 set of this part (Prius P1121: Coolant Flow Control Valve Position Sensor).
    Please give me your offer

  3. im interested in buying this part only prius p1121 coolant flow control valve position sensor. thank you.

  4. I had the engine light and red triangle come on. The code was p1122. 3 way valve. I replaced valve and it fixed prob. BUT about 6 months later came back again. This time I found that The dealer who checks all fluids must have missed radiator. Filled it up and fixed again. BUT another month and engine light on again p1121. Now what? I can’t see anything else wrong. Valve again? What about a temp sensor? Is their on in that system?
    HELP!

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