With a diesel, inaccurate OBC fuel consumption readings suggest that the engine may have had an aftermarket chip installed. Considering that the vehicle is new to you, are you aware of any engine modifications? If so, removing them may correct the fuel consumption indication.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue