Abstract: The invention relates to a method for operating a fuel injection system (1) for supplying a combustion engine of a vehicle with fuel, in which method the fuel is conveyed at high pressure with the aid of a high-pressure pump (2), fed to a high-pressure accumulator (3), and injected into a cylinder of the combustion engine with the aid of at least one injector connected to the high-pressure accumulator (3). In order to detect any damage to the drive of the high-pressure pump (3), according to the invention a) the pressure (P) in the high-pressure accumulator (3) is measured and, on the basis of the measured values, a pressure drop (?P) in the high-pressure accumulator (3) caused by an injection into a cylinder is determined, b) a maximum pressure gradient is determined during a pressure build-up phase following the injection, c) the determined pressure drop (?P) and the determined maximum pressure gradient are put into proportion.