An adjustment drive of a motor vehicle, in particular for an electromotively operated tailgate, having an adjustable part. A drive unit has a first drive train and a second drive train. Each drive train has a variable-length actuation part attached to the adjustable part. The actuation part is driven by an electric motor of the respective drive train. The first drive train has at least one sensor for detection of a position of a rotating part, and the second drive train has no more than one sensor for detection of a position of a rotating part. We also describe a drive unit of an adjustment drive of a motor vehicle.