S90 rain light sensor fault

Interesting. I had a similar issue with my 2018 Audi A4. Same symptoms: auto headlights, wipers, and dimming all went haywire. For me, it turned out to be bubbles forming under the gel pad of the windshield, right where the sensor sits. This was messing with the sensor's readings.

Bubbles under the gel pad? Interesting. Did you fix it yourself, or did you need professional help? Was it expensive?

I tried to fix it myself at first, but without the right tools, I made it worse. I'd recommend a workshop. The diagnostic effort should be minimal. The repair cost me 62€.

Thanks. Seems I have the same issue with the rain sensor. The problem was indeed caused by bubbles under the sensor's gel pad. I went to my local workshop as you suggested. They replaced the gel pad and recalibrated the sensor. Now, all systems are working.