BMW M4 Seat Belt Tensioner Issue, Help Needed

Hi there! I have some experience working on cars, and I actually faced a similar issue with my 2014 BMW M3 last year. The belt handover system failed on the driver's side, super annoying when it stopped working. Took it to my workshop and they diagnosed a faulty belt bringer motor unit. Total repair cost me around 455 Euro, but it's been working perfectly since then. In my case, they had to replace the entire handover mechanism. What's the exact error code you're getting? Also, is it happening on both sides or just one side? Knowing these details would help me share more specific insights from my experience.

Thanks for sharing your experience! Good to hear you managed to fix a similar issue. In my case, the error only shows up on the passenger side, and I'm getting error code 93AC18. The handover just stays retracted and doesn't come forward at all when opening the door. At 75734 KM and just after my latest service, I wasn't expecting to deal with something like this. Did your workshop mention if this is a known issue with these cars? Also curious if there's any temporary fix I could try before taking it in.

Hey again! Thanks for those extra details about your M4. Yeah, that's definitely the same behavior I experienced with my M3, though mine was on the driver's side. The error code you're getting (93AC18) is exactly what popped up on mine too, talk about déjà vu! From what I recall, my mechanic mentioned these belt handover systems are actually quite common failure points in our cars, especially around the 70-80K mark. He showed me that the motor unit tends to wear out over time, regardless of how well you maintain the car. Super frustrating, I know. Unfortunately, there's not really any DIY fix for this, I tried fiddling with mine before taking it in, but these systems are pretty complex. One thing though, check if your fuses are all good, but honestly, given the error code and symptoms, it's likely the motor unit like mine was. Quick note, since you mentioned yours happened right after a service, might be worth checking if anything got disconnected during the work. My mechanic mentioned they sometimes need to remove panels near the belt system during routine maintenance, and sometimes connections can get a bit loose. Keep us posted on what you find out when you get it checked!

Thanks for all that detailed info! Really helpful to know it's a common issue around this mileage. I actually checked the fuses as you suggested, all seem fine, and I also looked for any loose connections but couldn't spot anything obvious. I've booked it in for next week at my regular workshop. Given what you've shared about your experience, I'll make sure to specifically mention the motor unit to them. The price you mentioned gives me a good idea of what to expect too, which is super helpful for planning. Will definitely update once it's sorted. Really appreciate you taking the time to share your experience with this, it's always more reassuring when someone's dealt with the same exact problem before!