S5 Transmission Failure: TCU Problems and Grinding Gears

I dealt with very similar transmission issues on my 2006 S4 last year, and I have some experience with transmission repairs. The symptoms you describe match closely with what I experienced, rough shifting, grinding, limp mode and transmission control problems. After proper transmission diagnosis at my workshop, they confirmed a defective control unit was causing the erratic behavior. The repair involved: Complete transmission control unit replacement, Software update for the car computer, Transmission fluid change and system reset Total repair cost was 1000 Euro which included parts and labor. The gearbox issues were completely resolved after fixing the control unit. Shifting returned to normal, no more grinding or slipping. Before suggesting specific solutions, could you share: Current mileage on your S5? Any transmission service history? Are there any other warning lights besides check engine? Have you scanned for error codes? This information would help determine if your situation requires similar transmission repair steps or if other components might be involved. Based on your symptoms, its likely related to the transmission control system, but best to confirm with proper diagnosis.

Thanks for the detailed response. My S5 has 197249 KM on the odometer with the last transmission service done at 180000 KM. The automatic gearbox started showing these symptoms quite suddenly. I scanned the ECU and got error codes related to the transmission control module. Currently only showing the check engine light, no other warning indicators. The repair costs you mentioned are encouraging, as I was worried about a complete transmission replacement. I will have the transmission diagnosis done at a workshop specializing in gearbox issues. Will update once I get the results. Your experience with the control unit replacement matches what others have suggested. Hoping my transmission problems can be resolved with similar repairs without major component replacement.

Thanks for providing those details. After you mentioned the mileage and recent service history, I am even more convinced your S5 has the same transmission control module issue I encountered. The sudden onset of symptoms and error codes from your automotive ECU scan pointing to the control module match the failure pattern I experienced. The timing also makes sense, these gearbox issues often appear between 180000-200000 KM even with proper maintenance. When my transmission diagnosis was done, the workshop confirmed the control module was sending incorrect signals, causing the erratic shifting. Since your symptoms mirror mine exactly, especially the grinding noises and paddle shifter response problems, I strongly suspect the same root cause. The good news is these transmission problems are often fixable without major mechanical work. In my case, once the faulty transmission control unit was replaced and reprogrammed, the gearbox returned to normal operation with: Smooth gear changes, Properly functioning paddle shifters, No more emergency mode, Resolved error codes My advice would be to proceed with the specialized workshop diagnosis. If they confirm the control module failure, you are likely looking at a similar 1000 Euro repair range rather than a full transmission replacement.

I appreciate the thorough information and your similar experience with transmission control issues. Having complete transmission service records and scan data will definitely help the workshop diagnose my gearbox problems more efficiently. The confirmation that these automatic gearbox symptoms typically appear around my mileage range is helpful. Knowing your transmission repair was resolved without major mechanical work gives me confidence to proceed with the diagnostic testing. Based on the matching symptoms, especially the grinding, slipping and paddle shifter failures, I feel more optimistic that my S5 might just need the control module replaced rather than extensive transmission repairs. I have scheduled an appointment with a workshop that specializes in gearbox issues for next week. Will have them perform a complete transmission diagnosis focusing on the control unit. The potential 1000 Euro repair cost is much more manageable than I initially feared. Will post an update once I get the workshop results and know exactly what repairs are needed to resolve these transmission problems. Thanks again for sharing your repair experience, it has been extremely helpful in understanding what I might be dealing with.