The invention relates to a method and a device for detecting and characterizing fuel leakage in an injection system of an internal combustion, which more particularly is not in operation, and a vehicle having such a device. The injection system has an injection device for injecting fuel into a combustion chamber of the internal combustion engine, a closable high-pressure branch for supplying the injection device with fuel placed under a first fuel pressure, and a closable low-pressure branch for feeding fuel placed under a second, lower fuel pressure from a fuel supply to the high-pressure branch. The high-pressure branch and the low-pressure branch are each closed, wherein in the high-branch branch and in the low-pressure branch an associated curve of fuel pressure over time is sensed at the same time during a measurement time period. On the basis of the sensed curve of fuel pressure of the high-pressure branch, it is checked whether fuel loss occurred in the closed-off high-pressure branch during the measurement time period. By means of the sensed curve of fuel pressure of the low-pressure branch, it is checked whether a flow of fuel into the closed-off low-pressure branch occurred during the measurement time period. Furthermore, if the existence of fuel loss was determined in the first checking step and additionally it was determined in the second checking step that no flow of fuel into the low-pressure branch occurred, a signal is output, which indicates fuel leakage from the high-pressure branch into the combustion chamber.