ISO 14229 UDS protocol: Automotive diagnostics

The UDS (Unified Diagnostic Services) protocol is defined in the ISO 14229 series. Automobile OEMs (original equipment manufacturer) follow this standard to provide a common computer system that can be used to diagnose any vehicle.

The complete article is published in the June issue of the CAN Newsletter magazine 2022. This is just an excerpt.

The automotive industry is drastically evolving, with the main reasons behind this evolution being the increased need for safety and improved driving experience. Cars on the road today contain 40 to 150 individual ECUs (electronic control unit), each performing specific functions such as electronic fuel injection (EFI), engine control, door locks, braking, window operation, and more. Increased complexity requires more efficient ways to test and diagnose vehicle systems when a fault occurs. There have been many diagnostic protocols such as KWP2000, ISO 15765, and K-Line developed over time for vehicle diagnostics.

So, to ensure universal compatibility, OEMs and suppliers agreed to rely on a standard protocol which is named as UDS protocol. UDS is the latest automotive vehicle diagnostic protocol used to diagnose vehicles worldwide. This protocol is defined in the ISO 14229 standard and automobile OEMs follow this standard to provide a common computer system that can be used to diagnose any vehicle.

Architecture of UDS protocol

Nowadays, the utilization of the protocol is increasing due to its flexibility. This protocol is derived from the ISO 14230-3 (KWP2000) and ISO 15765-3 (Diagnostic Communication over CAN (DoCAN)). It is used for the vehicle diagnostic, ECU firmware flashing, and many more such functions. The UDS protocol uses fifth (session layer) and seventh (application layer) layer of the OSI model while the CAN protocol works on the first (physical layer - ISO 11898-2) and second (data link layer - ISO 11898-2) layer of the OSI model.

Diagnostics in a vehicle

The protocol is defined for two types of devices, namely, server and client. The vehicle will be the server and the diagnostic device will be the client. Recent vehicles are equipped with a diagnostic interface, which makes it possible to connect a computer or diagnostics tool, to the communication system of the vehicle (ECU). UDS requests are sent to the controllers, which provide a positive or negative response. With these responses provided from the controller it is possible to diagnose faults and undesirable behavior inside vehicles such as:

• Data stored within the system
• Memory available in the individual control units
• Live vehicle data such as engine or vehicle speed
• Firmware updates
• Interaction with hardware I/O to turn specific output on or off based on the response to identify the fault
• Run specific functions to understand the environment and operating conditions of an ECU

Diagnostic services of UDS protocol stack

IWave offers the UDS protocol stack, which is compliant with the ISO 14229 standard and implements both the application layer (ISO 14229-1) and session layer (ISO 14229-2). The UDS stack enables diagnostics such as UDSonCAN and UDSonIP for both client and server implementations.

If you would like to read the full article, you can download it free of charge or you download the entire magazine.

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