Engine and electrical failure while driving!

[Greg125i]

Hey all
I'm hoping someone can help me here because so far BMW can't! I was driving (2011 125i M Sport convertible) along the other day and was only going about 15mph when everything just died, electrics and engine (first thing I noticed was my lights cut out as it was dark!). So I coasted to the best place I could and there were lots of warning lights (sorry I'm not technical but I remember the picture of the steering wheel and exclamation mark to the right). I pressed the ignition to restart but at that point there was no life at all, zero reaction, not even warning lights. Now that part has happened before when trying to start the car, the whole no life thing but not while driving, and I knew that I just had to wait a minute. So I did the same again and it did indeed come back to life, as if nothing had ever happened and it hadn't just tried to kill me! No warning lights, nothing! So luckily I was one road from home and I drove there, but the car ran perfectly... The next day I called the BMW assistance and they sent a technician who couldn't find ANYTHING. Zero fault codes apart from one for the roof, car ran beautifully, battery charges fine, connections seem fine on the surface, we drove it for a few mins and nothing. So fair enough, he couldn't do anything if he can't find anything but does anyone have any idea what could be going on please? On a side note, as I was putting the car back in the garage after the technician left, the Windows wouldn't go down and up when opening and closing the door. But again it only lasted a while... So apologies for the long post but I'm throwing as much info out as I can and if anyone can help I'd really appreciate it! Thanks in advance!

[Dackelone]

Is the charging system Ok? Maybe loose battery terminals or a bad battery(internal short). How old is the battery? These are just guesses really.

Has thee been any other repairs recently? Like maybe an accident/body shop?

I am sure your dealer will find the culprit.

[Greg125i]

Yeah the battery is charging fine but at the same time it shouldn't be the battery or even alternator if it was while driving, right? Oh also, while I was stopped with no life in the car, I did have the hazards on, which also suggests something strange non-battery related? Cheers!

[Greg125i]

Not sure how old the battery is but I only bought it from the main dealer in April. No accidents or anything, it's treated well, by me anyway! Not sure about precious owner treatment but you assume main dealers only sell the good ones...or I do anyway!

[Dackelone]

It kind of sounds like a bad alternator to me. IF you still have the original battery... I would start there. And be sure to have it coded to the car.

[Greg125i]

Thanks for your reply. The technician who can me out seemed to think it couldn't be the alternator or battery as they shouldn't cause it to cut out while on the move as the engine is already running. Is that not the case?