SEN0189 turbidity sensor cabling

Hi all,

I am using a SEN0189 turbidity sensor and for whatever liquid the sensor contacts (clean, dirty, high opacity) the signal on the blue output wire gives always 4.05 vdc. As advised, I have checked the probe connection cable and it is correct. The interface is powered with 5 vdc and the switch is on the A position. What could I have missed except a defective hardware ?

Is the light of the photo sensor supposed to be visible ? As far as my sensor is concerned, the light is not visible or not lit on which could be the problem.

Thank you for your help.