If the car has been disconnected from power for a while then it could be the alarm system has become un-synced from the DME so its automatically cutting power to the pump, if this is the case you'll need the BMW software like ISTA to re-sync them, also the battery will need to be registered.
Throw a post up in this forum listing as much detail as you can so they can give you the best advise :thumbup:.
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