What engine do you have? Troubleshooting needed to hone in on the problem can be many causes. The first troubleshooting I would do is monitor fuel pressure at the schrader valve and see if fuel pressure is there when it dies. What codes have you seen? Does it happen regardless of the amount of fuel in the tank?

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas