A method of controlling a powertrain of a vehicle includes opening and/or closing one or more of a first switching device, a second switching device, a third switching device, and engaging and/or disengaging at least one of a pair of actuators for a starter mechanism or a motor/generator clutch. Many different control modes are provided for the powertrain by changing the operation of a motor-generator between a motor or a generator, and changing the electrical connections between a first energy storage device, a second energy storage device, an auxiliary electric system, the starter mechanism, and the motor-generator.