Abstract: A hydraulic unit of a traction control system of a hydraulic vehicle brake system includes a hydraulic block and an electric motor that is arranged on the hydraulic block and configured to drive hydraulic pumps of the traction control system. The hydraulic block has a valve side that faces away from the electric motor. Solenoid valves, an electronic control unit and electrical plug contacts in a multiple electrical connector are arranged on the valve side. In order to prevent any liquid that has leaked from the electric motor from reaching the valve side, a hollow shaft, through which connection lines of the electric motor are fed, is sealed in a through-hole, which runs from the electric motor to the valve side facing away, by a sealing ring that consists of acrylonitrile butadiene rubber that swells upon contact with brake fluid.