Abstract: A system for preventing vibrations occurring in a diesel engine during shut down. The system employs a combined starter/alternator apparatus to apply a positive and/or negative torque to an engine to effect a smooth deceleration of the rotating parts of the engine. A system control function is provided wherein the engine speed from a vehicle engine speed sensor and the vehicle ignition key off signal are introduced to a control means to determine if the rate of engine speed deceleration is above or below a selected threshold level. If the rate of deceleration is above the selected threshold level, a command is generated by the control means to cause power to be absorbed from a rotating part of the engine to slow the engine. If the rate of engine deceleration is below the selected threshold level, a command is generated to add torque to the engine rotating part to prevent rapid deceleration.