The invention provides a method and device for characterizing a vehicle's fuel efficiency and amount of fuel consumed. The method features the steps of: 1) generating a data set from the vehicle that includes vehicle speed, odometer calculation, engine speed, load, mass air flow; 2) transferring the data set to a wireless appliance that includes i) a microprocessor, and ii) a wireless transmitter in electrical contact with the microprocessor; 3) transmitting a data packet comprising the data set or a version thereof with the wireless transmitter over an airlink to a host computer system; and 4) analyzing the data set with the host computer system to determine a status of the vehicle's fuel efficiency.