Audi S6 Security System Prevents Engine Start

Having experienced similar symptoms with my 2016 Audi A6 3.0 TDI, this sounds like a typical immobilizer fault where the key signal is not being properly recognized by the anti-theft system. The constant security light and intermittent starting issues match what happened in my case. The root cause was a fault in the key programming system, not the key itself. The immobilizer control unit had lost synchronization with the key transponder. This required specialized diagnostic equipment to reprogram the system and restore proper communication between the key and the immobilizer. It was a serious issue that could not be fixed with basic tools or DIY methods. The fix involved: Full system diagnostic scan, Immobilizer control unit reset, Key signal verification, Complete reprogramming of the key-to-car communication While the repair was complex, requiring specific dealer-level equipment, it fully resolved the security light and starting issues. The symptoms you describe strongly suggest your S6 needs similar electronic intervention to restore proper anti-theft system function. Would recommend having this checked by an authorized service center with proper diagnostic capabilities, as incorrect programming attempts can make the situation worse.

Thanks for sharing your experience. This actually mirrors what I went through with mine. You definitely nailed the diagnosis, the key programming system being out of sync with the ignition control module sounds spot on. Can you recall roughly what the repair cost you? And have you had any security light issues or starting problems since the fix? Mine was done about 6 months ago and no issues so far, but always good to know what to expect long-term when dealing with car electronics like this.

Glad to confirm the diagnosis was accurate. Since having the immobilizer bypass and key reprogramming done, my car has been running perfectly with zero security light issues. The repair was surprisingly affordable at just 45 Euro for the complete ignition control system reset and key signal recalibration. The remote start function also works flawlessly now, which was an unexpected bonus. These car electronics can be tricky, but once properly reset and reprogrammed, they tend to stay reliable. Six months of trouble-free operation in your case is a good sign that the fix was done correctly. Just keep your spare key in good condition and avoid exposing the main key to strong magnetic fields or extreme temperatures to prevent future programming issues.

I finally got this sorted out and wanted to update everyone on my experience. After taking it to a specialized auto electronics shop, they confirmed it was indeed an immobilizer system fault. The whole repair process took about 2 hours. The technician had to perform a complete reset of the ignition control module and reprogram both my keys. Total cost came to 280 Euro, which included full diagnostic testing. More expensive than some quotes mentioned here, but worth it for the peace of mind. Car starts perfectly now and the security light behaves normally. Been running smoothly for 3 weeks with no anti-theft system warnings or starting issues. Really glad I chose a shop with proper diagnostic equipment rather than trying cheaper alternatives. For anyone facing similar problems, definitely get it checked by someone who specializes in car electronics and key programming. The extra cost for proper equipment and expertise makes a huge difference in the quality of the repair.