Those 6900727 airbag modules (used up to 4/2001) are notorious to cause problems. The internal chip gets corrupted showing internal fault and none of the active codes can be reset. The module can be repaired but but it needs to be done on a bench programming the chip.

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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