Failing Rain-Light Sensor Disrupts Multiple TT Features

I had this exact same electrical fault on my 2014 Audi A5 last winter. With some experience working on Audi electronics, I can share what happened. The malfunctioning sensor symptoms were identical, auto wipers, light sensor functions and display dimming all failed simultaneously. After inspection, it turned out bubbles had formed under the gel pad that connects the rain detection sensor to the windshield, causing multiple sensor fault codes. The fix involved replacing the entire sensor unit, since the gel pad deterioration meant the original sensor could no longer maintain proper contact. Total repair cost was 62 Euro including labor and parts. Key things to check before repair: Look closely at the sensor mount near your rearview mirror, Check if you can see any air gaps or separation, Verify if the sensor feels loose when gently touched Could you share: Whether you see any visible issues around the sensor area, If the problems started gradually or all at once, Your exact build month/year, as there was a known sensor batch issue, If you have any error codes stored that you can share This will help determine if your issue matches the common sensor fault pattern these models experienced.

Last service was at 182000km. After researching similar issues posted here, I checked the error codes at home. The diagnostic showed error code B103A for the light sensor and B103B for rain detection module. Both car components started failing around the same time. I inspected the sensor housing near the mirror and noticed slight separation around the edges. The auto sensor unit also moves slightly when touched, which seems unusual. The electrical fault appears consistently, the sensor systems either work incorrectly or not at all. Going to book it in for repair next week. Will update once fixed in case others experience similar issues.

Thanks for the update. Those error codes and symptoms exactly match what I encountered with my A5's sensor assembly. The movement you noticed in the auto sensor unit is a clear indication the gel pad has deteriorated, just like in my case. Some advice based on my repair experience: Make sure they replace the complete sensor unit, not just the gel pad, Request checking the windshield surface for any micro-damage while the car electronics are being serviced, Confirm the repair includes recalibration of the light sensor and rain detection systems My car now has 210000km and the replacement sensor has worked flawlessly for over a year. The electrical fault codes cleared immediately after installation and haven't returned. The repair cost might have increased since my fix, but knowing exactly what needs replacing should help avoid unnecessary diagnostic time. Let us know how the repair goes, tracking these common issues helps other owners identify similar problems early. Looking forward to hearing if your fix resolves all the sensor-related symptoms like it did in my case.

Thanks for the input. Quick update after getting the car back from the workshop today: The diagnosis confirmed the sensor calibration issue matched what was discussed. They found the gel pad had completely separated from the windscreen, causing all those electrical fault codes. The entire sensor unit needed replacement as suggested. Final repair cost was 85 Euro including parts and labor. All car electronics are now working perfectly, auto wipers respond correctly, headlight control is restored, and the speedometer dimming works as it should. The car components were properly calibrated after installation. Really glad I checked here first, saved time on diagnostics since I could point them directly to the failing sensor unit. The separation around the edges was indeed the key symptom of the deteriorated gel pad. Will monitor how the new sensor performs over the next few months, but so far everything is working exactly as it should.