Smart ForTwo Anti-Theft System Failure & Troubleshooting Fix

Having some experience with electrical systems, I faced a similar issue with my 2021 Smart EQ Forfour. The car alarm system showed identical symptoms, complete failure and error codes stored in the system. The anti-theft system problem turned out to be related to the alarm control module getting incorrectly coded after a software update. The immobilizer was still working, but the rest of the security features were compromised. My workshop ran a complete diagnostic on the alarm sensor network and found that the system needed to be recoded. The fix involved reprogramming the alarm control unit to properly activate the optical locking signals through the indicators. Total repair time was about an hour and cost 45€ for the programming. To provide more specific guidance for your case, could you share: Have you noticed any other electrical issues? Did this start after a dealer service or software update? Are you getting any specific error codes? Does the immobilizer still work properly? The car alarm systems in these Smart EVs are quite similar, so knowing these details would help determine if your issue matches what I experienced.

Just had my latest service done at 172509 KM and they checked the security alarm system. Can confirm this was not a battery issue or false alarm trigger. The problem seems more complex than a simple coding error. The onboard diagnostics showed multiple sensor communication failures. Your mention of the optical locking signals matches my symptoms exactly. Getting similar error codes related to the anti-theft control module. Running the full system scan revealed the alarm control unit needs replacement, not just reprogramming. Parts department quoted 380€ for the new unit. Good to hear your fix was simpler and cheaper, but unfortunately my case appears to need hardware replacement. Was hoping for a software solution like yours, but the failed communication tests point to faulty hardware. Will proceed with the control unit replacement next week.

Thanks for the update on your Smart Fortwo situation. After you mentioned the sensor communication failures, it reminded me to check my service records. Initially I thought my issue was resolved with just the programming, but I actually had a follow-up repair a few weeks later. The anti-theft control module showed intermittent communication errors even after the initial fix. The alarm system would work temporarily but then fail again. My repair also ended up requiring a complete control unit replacement, similar to what youre facing. The total cost aligned with your quote, around 365€ for the part and labor. While the price seems steep, the new control unit completely resolved the alarm system failures and prevented any false triggers that could drain the battery. A helpful tip: make sure they verify all sensor connections during installation. My technician found some corroded pins in the wiring harness that could have caused issues with the new unit. The immobilizer integration also needed careful calibration to work properly with the new hardware. Worth noting that after the replacement, the system needed about 3 start cycles to fully initialize all security features. So dont worry if the alarm system doesnt respond immediately after the repair.

Thanks for that detailed feedback on the control unit replacement. After checking with my service advisor today, we scheduled the repair for next week. They confirmed the full system diagnostic results that show the security alarm failures arent fixable with just reprogramming. The 380€ price tag is steep but matches what others paid for similar repairs. Good point about the wiring harness check, I specifically asked them to inspect all connections during the installation since my car alarm started acting intermittently before failing completely. The service department mentioned the same thing about the initialization period for the anti-theft system. They said to expect multiple start cycles before all alarm system functions become fully operational. Will make sure to follow their guidance on testing the immobilizer and security features after the new control unit is installed. At least now I know what to expect with the repair process and recovery time. Really helpful to hear from someone who went through the exact same issue and got it properly resolved with the hardware replacement.