A power sliding door assembly for a motor vehicle comprising a door structure constructed and arranged to be mounted on a motor vehicle for movement between closed and opened positions and a drive assembly mounted on the door structure. The drive assembly includes a rotatable gear engageable with a gear track provided on the vehicle. The rotatable gear is drivable in a one direction to effect movement of the door towards the opened position and drivable in an opposite direction to effect movement of the door structure towards the closed position. A drive shaft is coupled with the drive assembly and is constructed and arranged to rotatably drive the rotatable gear. A reversible motor is mounted on said door structure and is energizable to drive the drive shaft in a first direction to enable the drive shaft to drive the rotatable gear in the one direction, and energizable to drive the drive shaft in a second direction opposite the first direction to enable the drive shaft to drive the rotatable gear in the opposite direction. A clutch assembly is provided that is constructed and arranged to selectively couple the reversible motor with the drive shaft, so that the reversible motor is coupled to the drive shaft when energized to rotate the drive shaft in either of the first and second directions, and so that the reversible motor is de-coupled from the drive shaft to prevent back-driving of the motor when the door structure is manually moved between the opened and closed positions.