Mercedes C Klasse rain light sensor fault

I understand you are experiencing difficulties with your Mercedes-Benz C Klasse rain-light sensor. I encountered a similar situation with my previous vehicle, a Volvo V70. The symptoms you describe, automatic headlight activation and the rain sensor malfunction, suggest a compromised light sensor functionality. Have you attempted sensor calibration?

Calibration? How involved is that? Is it like tuning a radio, or more like brain surgery? I'm guessing I need special tools?

The calibration process is similar to aligning the mirrors on a telescope, it requires precision. The malfunctioning sensor in my Volvo was eventually traced to the auto sensor being unable to properly read the incoming light. The workshop suggested the bubbling under the gel pad is likely interfering with the sensor. It is advisable to seek professional assistance to diagnose and rectify the issue.

Thanks for the info. Turns out you were spot on. Took it to the shop; bubbling gel pad. New sensor, 62€, all fixed.