P1121 2004 TOYOTA PRIUS Possible Causes
- Coolant flow control valve (cooling system stuck or clogged)
- Faulty coolant flow control valve position sensor
- Coolant flow control valve position sensor harness is open or short-circuited
- Poor electrical connection in the coolant flow control valve position sensor circuit
- Faulty engine control module (ECM)
How to Fix P1121 2004 TOYOTA PRIUS Code?
Start by checking the “possible causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
Check engine light on (or service engine soon warning light)
P1121 2004 TOYOTA PRIUS Meaning
The engine control module (ECM) monitors the water valve position based on the valve position signal sent by the water valve position sensor (potentiometer), which is coaxially coupled to the valve. The water valve performs three-stage control as shown above, and the ECM determines the valve position based on the voltage of each respective stage. To ensure proper monitoring of the water valve, the ECM checks for malfunctions by combining the potentiometer output and the coolant heat storage tank (CHS) outlet temperature sensor. If no change occurs in the valve position signal input to the ECM, or if the water valve response signal is very slow, even though the ECM commands the water valve motor to operate, the ECM determines that a malfunction has occurred in the water valve position sensor circuit and sets a diagnostic trouble code (DTC).