Audi Q7 No-Start: Immobilizer & Key Signal Issues Fix

I had a similar issue with my 2009 Audi Q5 3.2 FSI. Having some experience with car electronics and immobilizer systems, I initially tried basic troubleshooting before seeking professional help. The symptoms were nearly identical, intermittent starting issues and the engine cutting out shortly after starting. The immobilizer fault turned out to be related to incorrect key programming, which was causing communication issues between the key and the car's security system. The workshop diagnosed the problem using specialized diagnostic equipment and found that the key needed reprogramming. The entire process took about an hour and cost 45 Euro. Since the fix, the car has been starting perfectly with no further immobilizer-related issues. Before you head to a workshop, could you share: Have you recently replaced or had work done on the battery? Are you using the original key or a duplicate? Does the key fob work normally for locking/unlocking? Are there any other electrical issues present? This information would help identify if your issue matches what I experienced with the key programming problem or if its potentially a different immobilizer fault altogether.

Latest service was completed at 84100 KM, just 2 weeks ago. Thanks for your detailed response. The issue worsened after I replaced the battery last month. Im using the original key, and while the remote functions work fine for locking and unlocking, I notice a slight delay when turning the ignition. There are no other electrical problems that I can detect. I suspect the immobilizer bypass procedure might need to be performed after the battery change. The car electronics seem to be functioning normally otherwise, but the key signal could have been affected during the battery swap. Would reprogramming the key be necessary in this case, or could a simple immobilizer reset solve the problem?

Based on what you described, this definitely sounds like an immobilizer sync issue after the battery replacement. My Q5 showed similar symptoms when I changed the battery, the delay in ignition response is a classic sign of the key signal not being properly recognized. The immobilizer fault often occurs because the security system loses its settings during complete power loss. A simple immobilizer reset should resolve this without needing full key reprogramming. The reset procedure worked perfectly on my car without requiring the more expensive reprogramming service. For reference, my reset cost only 25 Euro compared to the 45 Euro for full key reprogramming. The process took about 15 minutes and completely resolved the starting issues and ignition delays. A few points to check before booking a service: Make sure the battery terminals are clean and properly connected, Try starting with your spare key if you have one, Clear any stored error codes if you have access to a diagnostic tool The remote start features should work normally after the reset. If you notice the key signal continues to have issues after the reset, then key reprogramming might be needed as a second step.

Thanks for the detailed advice about the immobilizer sync. You're right, I'll try checking the battery connections first and attempt starting with my spare key. The symptoms match exactly what you described with your Q5, especially the ignition delay issue. I've booked an appointment for tomorrow to get the immobilizer reset done. Given that all my remote start and door locking functions are working fine except for the slight delay in the security light response during ignition control, I'm hopeful the simple reset will fix it. The 25 Euro reset fee sounds much more reasonable than full reprogramming. I'll update the forum once it's resolved in case others face similar issues after a battery change. The key signal problems following battery replacement seem to be a common occurrence based on the responses here.