Methods and systems are provided for inferring a current operational state of one or more fuel tank grade vent valves. In one example, a method comprises predicting an upcoming fuel slosh event in a fuel tank positioned in a fuel system of a vehicle, and in response to such a prediction, sealing the fuel system within a threshold duration of the upcoming fuel slosh event and diagnosing a grade vent valve as a function of fuel level in the tank at the time of the fuel slosh event and a pressure monitored in the fuel system during the fuel slosh event. In this way, issues related to fuel tank overpressurization and/or release of undesired evaporative emissions to atmosphere may be reduced or avoided.