Is was the easiest thing to pull off the sensor and look if there was something broken, at least much easier than pulling out the jet and testing it. But I admit: Since I did not know exactly how the spray should look, I did not recognize the problem.
We disassembled the jet and found some debris in it - it must have entered when the water lines were unattached and open while we did some dirty mechanical work in the engine bay.
I have learned the lesson
Regards
Stefan