P1122 code

P1122 indicates that the water valve position signal is "low" - 0.2V or less. The factory service manual has more infp.

Ideally you would use your Prius compatible scan tool (such as Techstream) to look at engine ecu data for the water control (3-way) valve position and compare that the actual voltage at the valve connector (by "back probing" the wires while the valve is plugged in then meaduring with a digital multimeter ). Then figure out if the problem is a wiring fault (shorted to ground or open wire for the signal or the 5V reference), or if your new part is defective.

Or, if the code resets immediately after clearing, then you could try unplugging the valve, and plug in the old valve and see if P1122 no longer resets. That would point to a defective new part- did you get a Toyota part or aftermarket? Many aftermarket parts have reputations for poor reliability.


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