Some Audi A6 Quattro owners report experiencing issues with their gas and speedometer gauges not functioning, often attributed to a faulty sensor. Common causes include problems with the vehicle speed sensor (VSS), a malfunctioning speedometer, or electrical issues. A faulty speed sensor can lead to inaccurate speed readings, affecting fuel flow and ignition timing, and may result in erratic behavior or a complete stoppage of the speedometer. Additionally, issues with the sending unit, bad wiring in the gas indicator circuit, or problems in the speedometer circuit can impact the fuel gauge's functionality. In some instances, a malfunctioning speed sensor may even trigger the ABS light and cause the speedometer to stop working altogether. It is advisable for owners experiencing these issues to have the sensor checked and replaced if necessary to restore proper functionality.