K-Line: flexible solutions for a classic protocol

May 07, 2015 // By Peter Decker
In the past, the K-Line diagnostic protocol was the standard for diagnostic tasks in various vehicles, and it is still used widely used today.

The age of this interface has not made it obsolete in today's diagnostics, development projects and service tasks for modern hardware and software. That is because it can be used to cover a wide range of requirements: from simple communication with the ECU to the support of proprietary K-Line variants on the byte level and finally simulations of entire K-Line diagnostic testers and K-Line ECUs.

The K-Line diagnostic protocol no longer plays a substantial role in new developments, because systems such as CAN and Ethernet have long taken over diagnostic tasks once performed by the K-Line. Nonetheless, automotive OEMs, suppliers and service shops worldwide cannot overlook the fact that many vehicles and ECUs still use K-Line technology, and this will remain the situation for some time. ECUs with a K-Line interface are still used in passenger cars, the truck sector and in motorcycles.

Those presumed dead live longer

Millions of passenger cars and motorcycles with K-Line technology are still driving on the roads, especially in markets such as China, India and South Asia. They are generally vehicles whose level of technology is outdated by around 10 to 15 years. Many European vehicle developments of that time were and are still being built in Asia under license, although their production ceased many years ago here. It is still the usual practice – especially in cases of smaller production volumes – to continue to use proven ECU developments in subsequent or related product lines, and this too has extended the life of the K-Line.

Serial UART diagnostic protocol with bus characteristic

The K-Line is a diagnostic protocol that conforms to the ISO 14230 standard. Like the standard RS232 serial interface, it is based on the technology of typical UART (Universal Asynchronous Receiver Transmitter) circuits. In asynchronous transmission, the sender and receiver use start and stop bits for synchronization purposes.

This means that the system does not need a supplemental clock line, and a single-wire line suffices. In contrast to RS232, the K-Line – like a bus system – enables communication with different ECUs by addressing them. The standard transmission rate is 10,400 baud, and speeds up to 115.2 kbaud are used for such purposes as programming of flash memories.