Audi A5 Won't Start: Immobilizer Security Light Issue

The symptoms match exactly what happened with my 2014 Audi S5. The security light stayed on and the immobilizer fault prevented the engine from running properly. After proper diagnosis, it turned out the key transponder chip had lost its programming sync with the car anti-theft system. A dealership technician needed to reprogram the key using specialized diagnostic equipment. This was not a job for generic scanners or bypass solutions. The immobilizer system is tied directly to the engine control module, so bypass attempts often cause more problems. The repair involved: Full diagnostic scan of the immobilizer system, Key transponder verification, Remote start system check, Complete reprogramming of the key to the security system This was a serious issue requiring dealer-level equipment. The car was undriveable until fixed. Generic key programming or trying to bypass the factory anti-theft system would likely have caused permanent damage to the security modules. The most reliable fix is having the immobilizer and key properly reprogrammed at a shop with the correct diagnostic tools. Attempting cheaper alternatives risks damaging the whole system.

Thanks for sharing your experience. I had similar issues with my A5 last winter. The car electronics and immobilizer system were acting up in exactly the same way, security light staying on and engine cutting out. Good to know the key programming fixed it for you. Would you mind sharing what the total repair cost was? Also curious if youve had any repeat issues with the immobilizer or remote start system since getting it fixed?

Had the repair done last month and the immobilizer system has worked flawlessly since. The total cost was 45 Euro for reprogramming the key to sync properly with the car electronics. A fair price considering it completely resolved the security light and starting issues. The car anti-theft system now functions exactly as intended, no more problems with the engine cutting out or immobilizer fault codes showing up. The remote start works perfectly too, which confirms the key programming was the root cause. This repair proved much more straightforward and cost-effective than initially feared. The correct diagnostic approach saved both time and money versus trying immobilizer bypass methods that could have damaged the system permanently. No repeat issues whatsoever with the ignition control or security features. Would definitely recommend getting the key programming checked first if anyone experiences similar symptoms.

Thanks for the helpful advice. Took my A5 to a certified shop yesterday and you were right about the key programming being the issue. The mechanic found the transponder chip had degraded, causing the immobilizer fault and security light problems. The repair involved replacing the transponder and reprogramming it to match the car electronics. Total cost came to 120 Euro which included diagnostic time and the new chip. Much better than the 500 Euro quote I got from my previous mechanic who wanted to replace the entire immobilizer system. Car starts perfectly now and the security light functions normally. No more issues with the engine cutting out or fault codes appearing. The remote start is working smoothly too. Really glad I got a proper diagnosis instead of trying those bypass solutions I was considering.