To transmit data between an electric control unit (3) that has at least one operator element connection (6; 6.1, 6.2) and a diagnostic unit (7), the diagnostic unit (7) is designed to be connected to the operator element connection (6; 6.1, 6.2) and the control unit (3) is designed to switch over (17) from an operating signal receiving status into a data transmission mode in order to deliver data via the operator element connection.