The original German codes:

Gurtschloss Beifahrer/Fahrer (passenger/driver seat belt lock?)
Fehler aktuell vorhanden (error currently exists)
Masseschluss/Widerstand zu klein (short circuit/resistance too low)
Fehler nich sporadisch (error not sporadic)

To my understanding "Gurtschloss" is referring to a seat belt lock/buckle and at least image search is showing lots of pictures of buckles.

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09/2003 X5 3.0i
02/2003 X5 4.6is (non-runner)