Why is my fuel economy blank?

Fuel economy is the distance travelled divided by the fuel used to travel it. That can only be measured between two full tanks.

After your first full-tank fill-up, DriveIQ knows where the measurement starts but not yet how far you went. After the second full-tank fill-up, your economy appears — and it gets more accurate with every fill after that.

If you top up without filling completely, switch Full tank off. Those litres still count toward the next full-tank measurement, so nothing is lost.