A failed oil level sensor can turn on the oil level warning or not depending how it has failed. If there's no warning light on the dash you can ignore the fault code if you so choose and just remember to check the oil level and know that the only warning will come if the oil pressure drops. Though the OEM equivalent after market Hella sensor is not that expensive and renew it when the oil is changed and pan is empty anyways.

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey