Pressure-maintaining function in a fully hybrid drive

A method for maintaining and/or adjusting a system pressure in a fuel injection system of an internal combustion engine, in which the internal combustion engine is a part of an hybrid power train, which includes in addition at least one further drive. A system pressure in a reservoir element of the fuel injection system is monitored using a pressure sensor. In operating modes in which the internal combustion engine is shut down and/or is separated from the hybrid power train, the maintaining or the adjusting of the system pressure takes place via a pressure-regulating valve. The activation of the pressure-regulating valve takes place directly or indirectly via a control unit or a vehicle control unit or a clutch control unit.