Smart Roadster Won't Start, Immobilizer Issue Alert

I had a similar issue with my 2006 Smart ForTwo. Working on various cars as a hobby mechanic, I have some experience with security and starting problems. The symptoms match exactly what I encountered, security light staying on and engine cutting out, which pointed to the car immobilizer system not properly recognizing the key signal. The anti-theft system was preventing the engine from running normally. My workshop diagnosed it as an incorrect key programming issue. They had to resync the transponder chip in the key with the cars security module. The whole process took about an hour and cost 45€, which was reasonable considering the specialized equipment needed. Before taking it to the shop, I tried: Checking for damaged key fob battery, Cleaning the key and ignition lock contacts, Attempting to use the spare key To help diagnose your specific case, could you share: How many keys do you have for the vehicle? Did this start happening suddenly or gradually? Does the remote start function still work properly? Are there any other electrical issues present? This information would help determine if your problem is identical to what I experienced or if theres another underlying cause.

Last service completed at 124790 KM. The suggestions offered were very helpful, it ended up being exactly what they suspected. The car immobilizer was indeed the culprit, with the key signal failing to properly communicate with the security system. The workshop confirmed a faulty transponder chip in my main key. They performed a complete key programming reset and recoded both my keys to the vehicle. Total repair cost was 85€. The remote start and all security features now work perfectly. Important detail: They found slight corrosion on the key contacts which was interfering with the transponder signal. A proper cleaning of the contacts might help others with similar symptoms before investing in complete reprogramming. Would recommend others check their spare keys first and test the immobilizer with multiple keys if possible. This can help isolate whether its a single key issue or a system-wide car electronics problem.

Thanks for the update on your Smart Roadster issue. Had the exact same problem on mine last summer, and the immobilizer fault turned out to be more complex than initially thought. After your success with the key reprogramming, I wanted to add that my case required replacement of the immobilizer antenna ring around the ignition lock. The transponder chip was fine, but the antenna that reads it had degraded over time. The total fix ended up being 160€ including parts and labor. Good point about the contact corrosion. Wish I had checked that first, as its a common weak point in the Smart anti-theft system. For anyone else reading this thread, the immobilizer bypass procedure should always be left to professionals, as incorrect attempts can lock out the security system completely. The workshop mentioned they see this failure pattern quite often on our model year. Regular cleaning of the key contacts and checking the immobilizer antenna connections during routine maintenance can prevent similar issues from developing. Let us know if you experience any other starting issues. These first-gen Smart electronics can be tricky, but most problems are well documented now.

Thank you everyone for the helpful discussion. Just wanted to close this thread with a final update on my Smart Roadster starting issue. After 6 months since the key reprogramming repair, the ignition control system continues working flawlessly. The security light now behaves normally and the engine starts perfectly every time. The anti-theft system recognizes the key signal immediately. One additional tip from my experience: I now clean the key contacts monthly with electronic contact cleaner to prevent corrosion buildup. This simple maintenance seems to keep the immobilizer fault codes from returning. For reference, the total repair breakdown was: Diagnostic scan: 25€, Key reprogramming: 45€, Contact cleaning: 15€ Total cost: 85€ Much better than having to replace the entire security module or ignition system. Really appreciate all the suggestions that helped identify the issue accurately before the workshop visit. Best value was learning that key contact corrosion is a common trigger for these symptoms. Regular cleaning is now part of my maintenance routine to prevent future starting problems.