I have a e60 530d that will randomly cut out like you have switched it off at any speed. On the freeway or in a car park.
but as soon as you hit the start button again it fires and your away has any one else had this problem,
Battery connections - inc the one to rear of main fuse panel - but with Jake - see what codes it gives, all you know at the moment is you don't know enough...
Many many years ago I had a Rx7 (or wife did) and that started cutting out, all electrics still live, come to a halt and few mins later start fine and run fine till coupla days later cut out again....
That was the little sealing disc from a redex bottle that had been tipped into the petrol tank, it'd float around and every so often get sucked onto outbound fuel feed, car would stop and after a few mins float away, car start and be fine.
When we found it (tank out and drained on front grass) one 'person' remarked that the redex bottle had been leaking..... such is life