BMW 4-Series Battery Sensor vs Dead Battery Mystery

Hey there! I actually dealt with something very similar on my 2015 BMW 3 Series last month. The symptoms were exactly what you're describing, warning lights, difficult starts, and those annoying discharge warnings. Turned out my battery sensor was indeed defective. Had it checked at the garage, and they confirmed the battery itself was still in good condition. The faulty sensor was giving wrong readings to the car's computer system, causing all those warnings and starting issues. In my case, they had to replace both the sensor and its wiring harness as there was some corrosion build-up. It wasn't a major repair, but it's definitely not something you want to ignore as it can lead to bigger electrical system problems down the line. The fix sorted everything out, no more warning lights, car starts perfectly, and all electrical systems are working normally now. Make sure whoever checks it uses proper diagnostic equipment specific to BMW electronics.

Thanks for sharing your experience! That's really helpful as it sounds exactly like what I'm dealing with. I'm relieved to hear it wasn't anything more serious in your case. Could you remember roughly how much you ended up paying for the sensor and harness replacement? Also, has everything been running smoothly since the repair, or have you noticed any other electrical gremlins popping up?

Hey again! Happy to give you an update. I paid exactly 315 € for the sensor replacement and labor, and I can tell you it was money well spent! The mechanic did a thorough job with the battery sensor, and I haven't had a single electrical issue since then. It's been running like a charm, no more warning lights, no more struggling to start in the morning, and all the electrical systems are working perfectly. The dashboard is finally clear of those annoying battery discharge warnings. Even my headlights are back to their normal brightness. I'm really glad I got it sorted when I did because the mechanic mentioned that leaving it unfixed could've eventually caused problems with other electrical components. Honestly, it was such a relief to have it properly diagnosed and fixed. The car feels like new again! Just make sure whoever works on yours knows their way around BMW electrical systems, it makes a huge difference in getting it fixed right the first time.

Just got back from the mechanic, and I'm so glad I followed your advice! The repair went really smoothly, turned out you were spot on about the sensor being the culprit. My bill came to around 300 for parts and labor, pretty close to what you paid. The mechanic I found was great, really knew his stuff about BMW electronics. He showed me the old sensor and explained how it was giving false readings to the system. Got it all fixed in about two hours, and wow, what a difference! The car starts up instantly now, no more flickering lights or warning messages. Can't believe I was stressing about this so much! Thanks again for sharing your experience, it helped me know exactly what to expect and gave me confidence in getting it sorted. Here's hoping both our BMWs stay trouble-free for a good long while!