Smart Fortwo EV Shutdowns Linked to High-Voltage Issue

Had almost the exact same electrical fault with my 2020 Smart ForFour EV last winter. Having some experience with EVs, I first suspected a cable damage issue but it turned out to be more serious. After multiple system shutdowns and constant limp mode episodes, I took it to a certified EV workshop. Their diagnostic revealed a severe battery drain caused by a faulty cell module. The battery management system was trying to protect itself, hence the power limitations and shutdowns. The repair involved a thorough battery system diagnosis, cell testing, and ultimately replacing the defective module. Total cost came to 290€ including diagnostics and labor. Since the fix, no more system malfunction warnings or power issues. Before suggesting specific solutions, could you share: How many miles/kilometers on your battery? When did these symptoms first appear? Does it happen more during specific conditions (cold weather, after charging)? What charging setup are you using? This information would help determine if your case matches what I experienced or points to a different underlying issue.

Thanks for sharing the details of your ForFour case. My Fortwo currently has 194418 KM and had its last major service just 2 months ago. The voltage sensor readings started fluctuating right after a routine charging session last week. The battery warning light appears more frequently during acceleration, unlike your experience with constant system shutdowns. My electrical fault seems to follow a different pattern, occurring mainly during city driving rather than highway speeds. I will have the battery management system checked following your suggestion, though it sounds like my symptoms point to a different root cause than your cell module issue. The intermittent nature of my problem makes me suspect a connection or sensor issue rather than cell degradation. Going to schedule a diagnostic check to examine the specific battery warning codes. Hope the repair costs stay below what you experienced with your module replacement.

Really interesting how your symptoms differ from my ForFour case, especially with the acceleration-related warnings. After reading your description, I am also leaning more toward a voltage sensor or connection issue rather than cell degradation. In my follow-up research after my repair, I learned that intermittent electrical wiring issues often show up first during high-power demands like acceleration. The high-voltage system tends to be more stable during steady-state operation, which aligns with your highway vs city driving observation. The fact that your battery warning started right after charging suggests checking the charging port connections and related sensors. On my ForFour, the diagnostic revealed that seemingly minor connection issues can trigger the full battery protection protocol with similar symptoms. Since your mileage is significantly higher than when I had my issue, also worth having them inspect the main battery contactors. These can develop resistance over time, causing voltage fluctuations under load that trigger the system protection. The good news is that sensor and connection repairs typically cost much less than the cell module replacement I needed. Most voltage sensor replacements run between 150-200€ depending on location and labor rates.

I appreciate the detailed analysis comparing our cases. Those charging port connection and contactor inspection suggestions make a lot of sense given my symptoms. The voltage fluctuations during acceleration definitely point more toward a connection or sensor issue rather than actual cell problems. Having an inverter issue during high power demands but stable operation at steady speeds really matches what I am experiencing. Just checked my service records and noticed the battery warning codes started appearing exactly 3 days after that last charging session, which further supports your theory about checking the charging system connections. Will get it to the shop this week for a full diagnostic, focusing on the electrical wiring and sensor connections you mentioned. The 150-200€ estimate for sensor replacement sounds much more manageable than a full module repair. Will update once I have more info on the actual system malfunction causing these problems. Thanks for helping narrow down the likely causes. This should save some diagnostic time and hopefully keep the repair costs reasonable compared to your module replacement case.