rain windshild and light sensor

[X5Sport]

I'm just in the process of going through the same issue following a windscreen change last week. It was done by my insurers appointed team and they fitted the wrong screen (the light sensor prism module is a different shape), and damaged the prism bonded to the screen. The fitters actually cheese wired the sensor prism off the old and new screens and tried to swap them over. The result is that the sensor window is now opaque and the lights are on all the time and the rain sensor wipers don't work.

I'm now having the windscreen replaced with a BMW original screen by my dealer at the insurers expense tomorrow.

The important bit to note is that the sensor prism MUST have an optically pure/clear connection to the glass. The rain sensor bouces infra-red light through the glass and measures the reflected (or is it refracted) light at the other end. Rasin on the glass changes this and the difference causes the auto wipers to work at an appropriate speed. If the connection between the sensor, prism and glass is anything other than perfect the system simply doesn't work.

You will probably be better to go back to the company that changed your screen and get them to replace the screen and any other borken parts at their expense, or take it to BMW and get them to replace it, again at the glass repairers cost.

Hope this helps.