Citroen C4 rain light sensor fault

That sounds annoying. I had similar auto sensor issues with my 2018 BMW 3 series. Is the rain detection not working at all? Did you try to calibrate the sensor?

By 'rain detection', do you mean the automatic activation of the windshield wipers? If so, then yes, that's correct. I haven't attempted any sensor calibration myself. What does 'calibrate' mean here?

Yes, I was referring to the windshield wipers. Calibration involves adjusting the sensor's sensitivity. However, these malfunctions usually require professional assessment. The light switch symptom seems peculiar and might indicate a more complex issue. You should visit a workshop.

After visiting the workshop, it turned out bubbles had formed under the gel pad of the windshield affecting the sensor, which caused the fault. Repair cost 62€.