Smart Forfour EV Dead Despite Good Battery, Fix Guide

Testing revealed similar symptoms on a 2017 Smart Fortwo EV. The starter solenoid failed to engage despite having power at the battery terminals. The ignition switch signals were present but not reaching the starter. The root cause turned out to be a faulty relay switch connection where the wiring harness meets the main control module. This created an open circuit preventing starter engagement. The component was buried deep in the electrical system, making it a complex repair requiring specialized diagnostic equipment. For your Forfour symptoms, focus on these areas: Have the relay switch connections tested, particularly around the starter circuit, Get the wiring harness inspected for any visible damage or loose connections, Verify the starter solenoid is receiving the activation signal, Check for any corrosion at the battery terminals despite appearing normal This was a serious electrical issue that could have led to complete system failure if left unaddressed. Consider having a full electrical diagnostic performed rather than replacing parts one by one. Note that these electrical gremlins often appear similar but can have different root causes. Professional testing equipment will identify the exact circuit breaking point.

Thanks for sharing that detailed response. Ive been experiencing the exact same symptoms with my Smart Forfour and was about to start replacing unusual parts. Good to know about checking the relay switch connections specifically. Could you share what the repair ended up costing? Just trying to budget appropriately since these electrical issues can get expensive. Also wondering if youve had any other electrical problems pop up since getting it fixed? My fuse box has been acting up lately too, so Im concerned there might be related issues I should address while its in the shop.

Really glad I could help point you in the right direction. After taking it back to the mechanic, they identified and fixed the Terminal 15 ignition positive interruption that was causing the starting problem. The repair came to 95€ for replacing a damaged cable connector at the relay switch. Since getting that fixed, the electrical system has been running perfectly with no additional issues. The original problem was isolated to that specific connection and wasnt related to the wider fuse box or power supply system. However, given your fuse box concerns, its worth having them check the voltage drop across all major circuits while they have the car. This can identify any developing issues before they cause problems. From my experience, these Smart EVs actually have quite reliable electrical systems once the root cause is properly diagnosed. The key is using proper diagnostic equipment to pinpoint the exact fault rather than the trial and error approach of swapping parts. The ignition switch and associated circuits are pretty robust on these models, so once properly repaired, you likely wont face similar issues again. Just make sure the repair shop fully tests the system after fixes are made.

Following up on my repair experience, took the car back to the mechanic yesterday. After seeing their diagnostic readout, turns out my starter solenoid was getting power but a damaged connector in the wiring harness was preventing the activation signal from reaching it properly. The repair itself wasnt too expensive, 280€ for parts and labor. They also did a full electrical system check while it was in and found no other issues with the fuse box or circuits. Pretty relieved it wasnt something more serious. The car starts perfectly now and all electrical systems are working as they should. Definitely glad I didnt try replacing unusual parts myself. Having them use proper diagnostic equipment to pinpoint the exact problem saved both time and money in the end. Thanks again for pointing me toward checking those relay connections, really helped narrow down where to look. The mechanics confirmed that was exactly where the fault was occurring.