K-Line – ISO 9141

The bidirectional one-wire bus is one of the first ways to access to control devices. The entire com­mu­ni­cation runs over only one wire and is used for data trans­mission according to ISO 9141 in the auto­motive industry. The bus serially receives and sends data via one data line each. The data is trans­mitted using half-duplex technology.

This means that the sending and receiving of messages does not happen at the same time, since both terminals operate on the same channel. If an L-line is used in addition to the K-line, data communication can also take place uni­di­rec­tionally, i. e. only in one di­re­ction. In the meantime, the K-Line is frequently replaced by a CAN bus, as it is considered to be more efficient and effec­tive in terms of the exhaust emission standard.


One application example is the on-board diagnosis of control units. The K-Line was already integrated as a standard in the first OBD standard and has been supported ever since. The communication between the control unit and the diagnostic module is ini­tial­ized using what is known as sti­mu­lation. There are two types of fast initialization and 5-baud initialization.