Being relatively new(ish) to BMW ownership, just over 2 years now, I'm curious to know a bit more about CBS.
Is it purely based on a set timescale/mileage basis, in particular the brakes?
I know that my rear pads have about as much meat left on them as Karen Carpenter & I have replacement disks/pads already in preparation but my CBS seems to think I have 4300 miles left in them (yeah, right). Is the calculation of that only based on when the CBS was last reset for the rear brakes & using BMW's best guess as to how long they will last? I'm guessing the wear sensor (assuming it's working) will only issue a warning when the pads are worn to the point of activating it but if & when that happens, will that then tell the CBS that they need replacing?
Reason I ask is that I can't reset the CBS for any of the service items, replacing the rear pads for example, until it decides that they are due. I know for a fact that the rear brakes need replacing but I'm just having a little experiment to see if the CBS does actually tell me before they get to the point of failure (no biggie if I suddenly get a metal-on-metal grind, I'll just off-road the car until the following weekend that I can replace the brakes & pinch the missuses car for the remainder of the week). Any other car I'd have done them by now but I'm curious to see how clever all this is so I'm playing a little waiting game.