BMW M3 Door Lock Failure: Key Fob & Battery Issues

Hey there! I have some experience working on BMWs and dealt with a similar issue on my 2004 BMW M5 last year. The symptoms you're describing sound very familiar. My door handles weren't responding and the key fob became unresponsive, just like yours. After taking it to my regular workshop, they found loose connections in the wiring harness near the driver's door. The cables had worn out over time and were causing those battery drain warnings. The fix wasn't too complex, they had to replace some damaged cables and secure the connections properly. Cost me around 95 Euro for the whole repair, including labor. Been working perfectly since then. Before I can give more specific advice, could you share if you've noticed any pattern when these issues occur? Like does it happen more after rain or car washes? Also, have you checked if this happens with both door handles or just one side?

Thanks for sharing your experience! I'm actually facing similar symptoms with my M3 which has just clocked 8003 KM since my last service. The weird thing is, these issues started showing up completely out of nowhere, not really connected to weather or washing. It's happening on both door handles actually. Really hoping it's just a wiring issue like in your case, as that repair cost sounds way more reasonable than what I was worried about. Did your mechanic mention any special diagnostic steps they took before finding those loose connections?

Hey again! Thanks for the follow-up about your M3. Yeah, I totally understand your concern, when these electrical gremlins pop up, it's always worrying. About the diagnostic steps, my mechanic actually started with a complete scan using their BMW diagnostic tool, which pinpointed the exact location of the current drain. They then did a thorough visual inspection of the wiring harness, particularly focusing on the door handles and the connections leading to the comfort access module. Interesting that yours is happening on both sides, mine started with just the driver's side before affecting the passenger side too. Since yours is showing up out of nowhere on both doors, it might be worth checking the central locking control module as well. My mechanic mentioned this could also cause similar symptoms, though thankfully that wasn't my issue. Just a heads up, while my repair was relatively cheap, prices can vary depending on what exactly needs fixing. The fact that both your doors are affected might mean it's a different root cause than what I had. Still, it's usually not as expensive as replacing the entire comfort access system. Have you noticed any other electrical quirks lately? Like interior lights acting up or central locking making unusual sounds? These details helped my mechanic narrow down the problem in my case.

Thanks for all that detailed info! Really helpful to know about the diagnostic process your mechanic used. Actually, now that you mention it, I have noticed the interior dome light flickering occasionally, especially when locking/unlocking. Didn't think it was related but that could be another clue. I'll definitely ask my mechanic to check the central locking control module along with the wiring harness inspection. Even if it ends up costing more than your repair, at least I have a better idea of what to expect and where to start looking. Really appreciate you taking the time to share your experience, gives me some peace of mind knowing these issues are fixable without breaking the bank. Will probably book it in for a check next week and hopefully get this sorted soon.