Audi A3 Won't Start: Immobilizer System Failure Fix

Having experienced a similar issue with my 2018 Audi A4 last year (some experience with car repairs), I can relate to this frustrating problem. The symptoms were identical, engine cutting out immediately and the immobilizer system causing starting issues. The root cause was incorrect key programming after replacing the battery in my key fob. The key signal wasnt being properly recognized by the immobilizer system. What seemed like a major mechanical issue was actually resolved through proper key programming at an authorized workshop. The total repair cost was 45 Euro, which covered the diagnostic check and reprogramming. No parts needed replacement, though initially I was worried about a faulty ignition control module. To provide more specific advice for your case, could you share: Has there been any recent work done on the key fob or battery replacement? Are you using the original key or a duplicate? Does the key immobilizer warning light stay on in the dashboard? Have you recently had any work done on the car electronics? These details would help determine if your issue is similar to what I encountered or if it requires a different approach to bypass the immobilizer problem.

Last service was done at 111439 KM with full documentation. Thanks for the detailed response about immobilizer issues. My original key has never been reprogrammed, and I have not replaced any batteries. The key immobilizer warning light flashes briefly then stays on solid. No recent electronics work has been done. The immobilizer fault seems to occur out of nowhere, sometimes the car starts fine, other times it wont start at all. Would checking the key signal strength be a good first diagnostic step before looking at bigger repairs?

Thanks for those details. My experience with the Audi A4 suggests checking key signal strength would definitely be a smart first step. After resolving my initial immobilizer fault, I actually encountered a similar intermittent starting issue a few months later. In my case, the problem was a degrading key transponder, even though the key battery was fine. The immobilizer system was getting inconsistent key signal readings, causing unusual starting failures. The solid warning light after flashing is a typical indicator of this issue. Quick troubleshooting steps that worked in my situation: Had the key signal strength tested (30 Euro diagnostic fee), Discovered weak transponder signal, Replaced transponder chip and reprogrammed key (185 Euro total) The unusual nature of your starting problem matches the symptoms of a failing transponder rather than a complete immobilizer system failure. This is actually good news, as full ignition control unit replacements can cost over 800 Euro. Before booking a service, try this: Hold the key extremely close to the ignition when starting. If the car starts more consistently this way, its likely confirming a weak key signal issue.

Thank you for the detailed explanation about key signal testing. Based on the symptoms you described, this does sound very similar to my situation. The behavior of the security light matches exactly what you mentioned too. I will try the close-key starting test you suggested and get the signal strength checked as a first step. Since my car has the original key and this is happening out of nowhere just like your case was, the transponder diagnosis makes sense. Good to know the testing is relatively affordable at 30 Euro, and even the full transponder replacement would be much better than replacing the entire ignition control system. I will schedule the diagnostic test this week. Glad I asked about this before assuming I needed major repairs. Will update once I know if the key signal test reveals similar transponder issues to what you found.