Abstract: A drive system of a plug-in hybrid vehicle includes: an internal combustion engine; an electrical machine; an electrochemical storage device, which is configured to supply the electrical machine with electrical energy; and a conditioning system. The conditioning system is configured to precondition the electrochemical storage device and has an electric heating element. the conditioning system is configured, before the start of a journey, to activate a preconditioning function of the internal combustion engine and to preheat a coolant of the internal combustion engine by time-controlled activation of the electric heating element.