2005 Grand Voyager Fuel Gauge inacurate
 

Just taken ownership of an 05 Grand Voyager, fill the tank up as soon as we get it, monitor the mileage and can't believe how many km's we're getting out of the tank, then BANG... car runs out of fuel with over 1/4 tank showing on the gauge and over 100kms to empty on overhead display.
What can I expect the problem to be..?