A vapor management system (10) includes a sense tube (47) disposed in a fuel tank (12). A differential pressure sensor (17) has one side connected to the sense tube and another side connected to a vapor cavity so that the pressure sensor can measure a differential pressure (DP) between a volume of the vapor cavity and a volume of the sense tube containing liquid fuel. A temperature sensor (26) is in the vapor cavity. A processor 1) receives DP and T measurements at certain time intervals to determine the temperature at time zero (To), the differential pressure at time zero (DPo), the temperature at a certain time (Tt), and the differential pressure at a certain time (DPt), and 2) when (Tt - To) is greater than a certain value, compares DPt to a certain differential pressure value.