VW Eos Won't Start, Immobilizer System Issue Alert

Had a similar issue with my 2010 VW Golf. Based on some experience working on VWs, those symptoms definitely point to an immobilizer system problem. The security light behavior and starting issues match exactly what I dealt with. My key needed reprogramming due to a fault in the ignition control module. The workshop connected their diagnostic tool to check the immobilizer status and found corrupted key data in the system. The fix was relatively straightforward, they performed a complete key programming procedure which took about 30 minutes. Total cost was 45€ for the programming service. Since then, no more starting problems or security light issues. Before suggesting specific fixes, could you share: Have you tried using your spare key? Does the security light flash or stay solid? What exact error codes did your scan tool show? Any recent electrical work or battery replacements? This would help determine if your Eos has the same immobilizer bypass issues I experienced with my Golf. These VW models share very similar security systems, so the fix might be comparable.

Thanks for the helpful information about the key programming. Looking at the error codes again, I got P0513 and P1743. The security light stays solid red rather than flashing. My spare key shows the same behavior. Had the car serviced just 2 weeks ago at 85746km where they also replaced the battery, but the starting issues only began 3 days ago. No other electrical work was done recently. The strange part is that the anti-theft system worked fine before the battery change. Makes me wonder if the new battery somehow affected the car immobilizer settings. Would definitely appreciate hearing if others had similar experiences after battery replacements in their VWs. Starting to think the workshop needs to do a fresh key programming like in your case.

Thanks for providing those additional details. After my previous experience with the key programming fix on my Golf, I can tell you that battery replacements can definitely trigger immobilizer faults in VW models. The error codes P0513 and P1743 are exactly what I saw when my immobilizer system lost its programming. The solid security light is another clear indicator that your car immobilizer is not properly recognizing the key signal. Since both keys show the same behavior, and this started after the battery change, its very likely the immobilizer control module lost its settings during the power interruption. My mechanic explained this is a known issue with VW security systems when the battery is disconnected. The fix should be similar to what worked on my Golf, a complete reprogramming of both keys and the immobilizer system. Make sure the workshop uses the latest programming software, as older versions sometimes fail to properly restore the ignition control settings. The price should be comparable to what I paid (45€), though some shops might charge more if they need to update their diagnostic software first. For reference, my Golf never had another immobilizer fault after the reprogramming, even through subsequent battery changes. The key is having the programming done correctly the first time.

Thanks for all the detailed feedback. Getting more convinced its definitely an immobilizer issue now, especially after hearing about your similar experience following a battery change. Just called the workshop and scheduled an appointment for tomorrow morning. They quoted 60€ for a complete key signal reprogramming service. A bit more than what you paid but still seems reasonable. Mentioned the error codes and security light behavior to them, and they agreed its likely related to the recent battery replacement affecting the car electronics. They said they have the latest VW diagnostic software and can handle both the immobilizer bypass and key programming in about an hour. Will report back on how it goes. Really hoping this fixes the starting problems like it did with your Golf. Just glad to know its probably not a more serious engine or ignition control issue. Thanks again for helping me narrow down the problem before taking it to the shop.