Smart Fortwo ABS Warning: Speed Sensor Mystery Solved

I had a similar issue with my 2019 Smart EQ Forfour. As someone with some experience working on EVs, I initially tried basic diagnostic steps before heading to the workshop. The speedometer and ABS warnings appeared simultaneously, which usually indicates either a sensor malfunction or control unit issues. After running several diagnostic scans, the workshop discovered the ABS control unit was defective and needed replacement. The total repair cost was 1000€, covering both parts and labor. While expensive, it completely resolved both the ABS and traction control issues. The input from multiple sensors was being misinterpreted by the faulty control unit, affecting both systems. To better assist with your specific case, could you share: Has the odometer been working correctly? Are you getting any other warning lights besides ABS? Have you noticed any unusual behavior with the regenerative braking? When did these symptoms first appear? These details would help determine if your issue matches what I experienced or if it might be a different problem requiring different solutions. A professional diagnostic scan would be the best next step to pinpoint whether its truly a sensor issue or potentially the control unit like in my case.

The dashboard started showing these symptoms right after my last service at 148317 KM. The speedometer is working fine, and the ECM isnt showing any other error codes besides the ABS fault. The only other warning light is the stability control indicator. The malfunction seems worse during wet conditions, which made me suspect its probably more than just a sensor issue. I did notice the ABS kicks in much earlier than usual during normal braking, almost like its getting incorrect input from somewhere. Your control unit theory makes sense, especially since multiple systems are affected. Will get it properly diagnosed before jumping to sensor replacement. The behavior during braking definitely points toward a control unit issue rather than just a faulty sensor.

Thanks for those additional details, those symptoms sound exactly like what I experienced with my Smart EQ Forfour before getting it fixed. The way your ABS is triggering prematurely during normal braking was a key indicator in my case too. The connection to wet conditions is particularly telling, my ABS control unit was also more noticeably problematic in wet weather. This matches the diagnostic pattern I encountered, where the unit was misinterpreting the input signals from multiple sensors rather than just having a single faulty sensor. After my repair, I learned that when the control unit fails, it often creates this cascade of symptoms: Early ABS activation, Traction control malfunction, Stability system warnings, Increased sensitivity in wet conditions A full diagnostic scan should be able to confirm if the control unit is the culprit. While the 1000€ repair cost was significant, it completely resolved all these issues in my case. The technician explained that replacing individual sensors wouldnt have fixed the core problem since the unit wasnt processing the sensor data correctly. Would definitely recommend getting the control unit checked before spending money on sensor replacements.

Based on the diagnostic scan results and your experience with the control unit replacement, I think youre right. My symptoms match up perfectly with what you described. The early ABS activation and problems in wet conditions are exactly what Im experiencing. Going to schedule a full diagnostic check focusing on the control unit rather than just the speed sensors. Even though the 1000€ repair cost is steep, it makes more sense than replacing sensors that might not fix the underlying issue. The fact that both the ABS and stability systems are acting up really points to a control unit problem with how its processing the input from multiple sensors. Will get this sorted soon since the traction issues are becoming more noticeable, especially in wet conditions. The ECM readings being mostly clear except for the ABS fault also fits with your experience. Thanks for helping me avoid the potential waste of time and money on sensor replacements when the control unit is likely the real problem.