C5 Rain Light Sensor Fault

That sounds remarkably familiar! I also have a C5, and I dealt with similar sensor-related issues. So many seemingly unrelated systems were affected! Was there ever any disruption of the windscreen? I read the error could be related to bubbles forming under the gel pad of the windshield where the sensor sits, impacting its proper operation, thus causing misreading issues with lights or speed.

That's interesting. No disruption of the windscreen but the bubbles sound like a plausible explanation considering all the issues I have. Did you ever have the sensor recalibrated or replaced, or was it just a matter of addressing the gel pad?

I am far from skilled in auto-electrical wizardry! I had to bring it to a workshop. In my case, after confirming that bubbles had indeed compromised the sensor's accuracy, they addressed the issue, as the sensor was still functional. I can provide details of that workshop if you want but it would be better to bring your car to a local professional who will look into the issue.

Thank you so much for the valuable insight! I've had the gel pad checked, and indeed, small bubbles had formed. After its replacement and sensor recalibration, all systems are functioning correctly again. The total cost was 62€. Appreciate your help!