US Patent 7204237 Evaporative system leak detection upon refueling

A loose or missing fuel cap detection method for an evaporative emission control system of an automotive vehicle detects a loose or missing fuel cap based in part on whether fuel level changed. The method determines whether the fuel level changed, which is indicative of a refueling event. The method then determines if one or more leaks are present. If the fuel level changed and one or more leaks are present, the method determines that the fuel cap is loose or missing.