They found that it's possible that a fuel tank vent line, over time, could get chaffed, and eventually leak. Not sure whether they will end up with some new clamps, rerouting, or what to eliminate that possibility. To date, there have not been any outright failures, but it was noticed by a dealer while doing some other work, and BMW is stopping all new, or traded in ones from being sold to prevent the possibility from occurring. If it was considered catastrophic, they'd request all owners to stop using their cars, but that has not happened. A fix should be available soon, and then the cars can be released for sale and a recall will then modify the existing fleet of owners to preclude the possibility of it happening.