X5 e53 3.0d - Fuel Range suddenly dropped.

[Salty_Dog]

For years when we fill up the fuel tank, we've got a Range of 999km on the OBC.
Actual range is around 1050 to 1100km on country roads.

For the last year, I've noticed after filling the fuel tank, the display only shows 754km.
Driving has not changed.

I'll admit, it hasn't had a fuel filter for 6 years + or an Air Filter for 4 years.
Oil and Oil Filter every 10,000ks

Currently on 265,850 km

Any ideas?

Fill up at the same Service Station
Driving patterns haven't changed.

Thank You