BMW M3 Power Seat Mystery: No Movement Despite Ignition

Hi there! I have some experience working on BMWs and dealt with a similar issue on my 2011 BMW M5 last year. The symptoms were exactly the same, power seats not responding and memory settings acting up. After taking it to my regular workshop, they diagnosed it as a heavily discharged/defective battery causing insufficient power for the seat modules. Was a bit surprised since my 335i never had such issues. The repair cost me around 290 Euro including parts and labor. They had to replace the battery and reset the seat control modules. After that, everything worked perfectly again. Before suggesting anything specific for your case, could you share: Are there any other electrical issues? When did this start happening? Does the battery warning light come on? Feel free to provide more details so I can help further!

Thanks for the detailed response! My M3 (184758 KM) just had its service last month and they didn't mention any battery issues. But you might be onto something because I've noticed the interior lights seem a bit dimmer lately. No battery warning light so far, but the seat problem started about two weeks ago. It was gradual, first the passenger side started acting up, then the driver's side followed. No other electrical problems except for a slightly slower power window operation. I'll get the battery checked first before diving into more complex repairs. Would be a relief if it's just that! Really don't want to deal with replacing the entire seat module.

Hey again! Thanks for those extra details about your M3. You know, after reading about the dimmer lights and slower windows, I'm even more convinced it's battery-related, just like what I experienced with my M5. Even though your car was just serviced, batteries can start acting up pretty quickly. Mine did the same thing, no warning light, but the symptoms were really similar to what you're describing. The gradual failure pattern is also super familiar, that's exactly how mine played out. One quick thing you can try: if you have a multimeter handy, check the battery voltage. Should be around 12.6V when the engine's off. Mine was reading way low at 11.8V when I had these issues. I still recommend getting it checked professionally, but I'd bet good money it's the battery. Much better than dealing with seat module replacements, trust me, been there! Let us know what you find out. These BMWs can be tricky with electrical stuff, but usually it's something straightforward like this.

Thanks so much for the follow-up! You've definitely made me feel better about this whole situation. I actually got my hands on a multimeter from my neighbor and tested the battery, it's showing 11.9V, pretty close to what you mentioned about yours. Looks like we're dealing with the same issue after all! I've already called my regular mechanic and booked it in for tomorrow morning. Really hoping it's just the battery like in your case. The 290 euro repair cost you mentioned sounds way better than what I was imagining for a full seat module replacement! I'll make sure to update this thread once I get it sorted, might help someone else with similar issues down the line. Really appreciate you taking the time to share your experience with the M5. These BMW electrical gremlins can be pretty scary until you figure out what's actually causing them!