Audi S5 Immobilizer Issue Causes No-Start Problem

Having low experience with car repairs, I faced a similar issue with my 2013 Audi S4. The security light kept flashing and the car would stall right after starting. After some research, I discovered it was an immobilizer fault causing the problems. The issue turned out to be incorrect key programming that was messing with the car immobilizer system. The workshop diagnosed it using their diagnostic tools and reprogrammed the key. The whole process took about an hour and cost 45 Euro. Since then, the remote start feature works perfectly and the car starts without any issues. The security system now recognizes the key properly every time. To help with your specific case, could you share: Does the security light stay on or flash? Have you recently changed or had work done on the key? Are you using the original key or a replacement? Does this happen with all keys you have for the vehicle? These details would help determine if your issue matches what I experienced and whether a similar fix might work for you.

Service History: Last maintenance at 112334 KM Thanks for the detailed reply. My security light flashes rapidly and this happens with both keys. Neither has been replaced or reprogrammed since I bought the car used 2 years ago. Your experience with the key signal issues sounds very similar to what I am dealing with. The immobilizer fault seems to be preventing normal operation just like in your case. Before spending money at a workshop, is there a way to verify if the anti-theft system is actually the root cause? I want to be certain since diagnostic fees alone can be costly.

I understand your concern about diagnostic costs. When I had this issue with my S4, I actually tried a few basic checks before going to the workshop that might help verify if its truly an immobilizer fault: 1. Clean the key fob contacts and try using fresh batteries in both keys. A weak key signal can trigger the anti-theft system. 2. Hold the key very close to the steering column while attempting to start. If it starts this way but not normally, its likely a key programming or signal issue. 3. Watch if the security light pattern changes when you insert different keys. In my case, both keys showed identical rapid flashing, which confirmed the immobilizer system was the common factor. These symptoms match exactly what I experienced before discovering the faulty car electronics were causing the immobilizer fault. While basic checks are helpful, I found that proper diagnostic equipment was ultimately needed to resolve the issue. The workshop charges for my key programming ended up being worth it since it fixed both the starting problem and anti-theft system issues completely. They can verify the exact cause before making repairs, which protects you from unnecessary work. Would you be able to try these checks and report back the results? It would help confirm if your issue matches my experience.

Thanks for sharing those checks. I tried all your suggestions and here are my findings: The behavior persists even after replacing batteries in both key fobs. When holding the key right next to the steering column, the engine still cuts out immediately. Both keys show the same rapid security light flashing pattern you described. These results seem to confirm an immobilizer fault affecting the whole system rather than just one key. Based on your experience, I think I will need professional diagnostics to properly resolve the key signal issues. My only remaining concern is finding a workshop that has experience specifically with Audi anti-theft systems. Getting this diagnosed and fixed correctly the first time would be worth the diagnostic fees instead of trying cheaper alternatives that might not work. Do you recall if your repair required any special equipment beyond standard diagnostic tools? Just trying to be prepared when I call workshops for quotes.