A method for powering up a DC distribution system in a hybrid vehicle power train, said power train comprising a relatively high voltage electric storage system used for electric propulsion or for assisting, an internal combustion engine for driving the vehicle, an electric motor/generator which can be driven by the internal combustion engine in propulsion mode or by vehicle wheels in regeneration mode via a transmission for driving the vehicle or for charging the electric storage system, a clutch device to connect the electric motor/generator to the internal combustion engine, a power electronics unit with a voltage regulator which is arranged to convert a three phase AC output from the electric motor/generator into DC output for driving electrical loads in the vehicle or charging the electric storage system, and which is also arranged to convert a DC output from the electric storage system into a three phase AC output for driving the electric motor/generator to propel the vehicle, is connected to the electric motor/generator, a capacitor as a reservoir capacitor used for eliminating current and voltage ripples during pre-charge of the system, and an electronic control unit for controlling the power train via a control bus which is connecting the electronic control unit to each component part of the power train, wherein the electric storage system and the electric motor/generator are connectable to one or more electrical loads for driving the vehicle, characterized in that at the time of powering up the DC distribution system, the electric storage system is disconnected from the power electronics and by the powering up comprising the sequential steps of - initializing internal combustion engine ignition by the electronic control unit in order to crank the internal combustion engine via a starter motor and an auxiliary battery; - initializing a diagnostics test of power train components prior to cranking the internal combustion engine; - cranking the internal combustion engine using the starter motor; - requesting pre-charge of the electrical loads from the power electronics unit subsequent to cranking the internal combustion engine, closing the clutch device and driving hereby the electric motor/generator; wherein a predetermined voltage is requested from the power electronics unit and the voltage regulator is controlled to enter a pre-charge mode to power up the DC distribution system; and pre-charge the electrical loads by electrical power generated by the electric motor/generator; - connecting the electric storage system to the electrical loads when the diagnostics test and the pre-charge are completed; - resuming normal operation for the power electronics unit after the powering up of the DC distribution system is completed. - initializing internal combustion engine ignition by the electronic control unit in order to crank the internal combustion engine via a starter motor and an auxiliary battery; - initializing a diagnostics test of power train components prior to cranking the internal combustion engine; - cranking the internal combustion engine using the starter motor; - requesting pre-charge of the electrical loads from the power electronics unit subsequent to cranking the internal combustion engine, closing the clutch device and driving hereby the electric motor/generator; wherein a predetermined voltage is requested from the power electronics unit and the voltage regulator is controlled to enter a pre-charge mode to power up the DC distribution system; and pre-charge the electrical loads by electrical power generated by the electric motor/generator; - connecting the electric storage system to the electrical loads when the diagnostics test and the pre-charge are completed; - resuming normal operation for the power electronics unit after the powering up of the DC distribution system is completed.