Unified Diagnostic Services (UDS) is a diagnostic communication protocol detailed in the ISO 14229-1 and is used in the ECUs (Electronic Control Units) of vehicles. It is similar to ISO 14230-3 (KWP2000) and ISO 15765-3 (Diagnostic Communication over Controller Area Network (DoCAN)).

The protocol is “unified” in the sense that it is used internationally across different companies and manufacturers. It is used in ECU software projects such as:

• Electronic fuel injection (EFI)
• Automatic gear box
• Anti-lock braking system
• Configurable engine mobilizer
• Key controls
• Wiper controls

UDS differs from the CAN protocol in a crucial way. The CAN protocol specifies the first and second layer of the OSI Model – that is the Physical Layer (ISO 11898-2) and the Data Link Layer (ISO 11898-2). UDS, however, also specifies the fifth (Session Layer) and seventh (Application Layer) layers of the OSI Model.

In today’s vehicles, a computer can be connected to the diagnostic interface and send and receive messages from individual controllers on the vehicle data bus. UDS allows for standarized communication both between these controllers and between the controllers and the external computer.

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