Smart Forfour Key System Failure, Antenna Fix Guide

Had the exact same situation with a 2009 Smart Fortwo CDI. The signal interference was causing the central locking system to malfunction and the car radio antenna was part of the problem. The main issue turned out to be the antenna mount in the rear bumper area where corrosion had developed on the connectors. When the antenna ring picks up interference, it can disrupt both the radio signal and the key fob communication. During repair, we found the antenna cable had worn through the protective coating where it passes through the body mount, creating a ground fault. The entire fm antenna assembly needed replacement, along with the wiring harness section that connects to the central locking control unit. This is actually a known weak point in these models. The repair requires removing the rear trim panels to access the antenna connection points. While not a serious mechanical issue, it can cause significant inconvenience with both starting and locking functions. Make sure the repair shop checks the complete signal path from the antenna to the control unit, not just the visible antenna parts. A proper diagnosis should include testing for parasitic current draw and signal strength at various points in the system.

Thanks for sharing those details about the antenna repair and signal interference fix. Your symptoms match what I experienced exactly. Did the repair hold up well since then? Would be really helpful to know the total cost too, as Im getting quotes all over the place for replacing the automotive antenna and checking the wiring. My mechanic mentioned possible radio signal issues even after fixing the antenna mount, so Im a bit concerned about recurring problems. Really appreciate any follow-up insights from your experience with the Smart repair.

The repair has held up great since getting it fixed last month. The automotive antenna system works perfectly now, no more signal interference with the central locking or starting issues. The repair shop identified a damaged cable connection near the antenna mount as the root cause, just like in your case. The total cost came to 95€ for replacing the faulty connector and checking all the wiring paths. This was actually less expensive than I initially feared. The radio signal comes through crystal clear now, and the key fob works flawlessly from a good distance. Your mechanic should focus on thoroughly testing the antenna connections rather than just swapping parts. A proper fix of the fm antenna wiring resolved all the issues in my case, both the central locking and radio reception problems. No recurring problems since the repair was completed. Make sure they check the complete signal path between the antenna and control unit. Getting this done right the first time prevents future headaches with the automotive antenna system.

Finally got my Smart fixed yesterday and wanted to share the outcome. My antenna repair experience turned out quite similar to yours. The mechanic found corrosion in the antenna mount connection, plus some damaged wiring near the body panel. Total repair came to 120€, which included replacing the fm antenna assembly and fixing the signal interference issues. They had to remove several trim pieces to properly access the wiring, but the work only took about 2 hours. The central locking now works perfectly and the engine starts right up with the key fob. No more radio signal problems either. Really glad I asked here first, helped me point the mechanic in the right direction and avoid unnecessary parts replacement. For anyone else facing similar issues, definitely worth checking the antenna connections first. Much cheaper than replacing the entire locking system like some shops suggested.