The difference between UDS and OBD protocols

Administrator posted this 30 May 2018

One of the most common questions from car lovers - «What is the difference between UDS and OBD».

UDS (Unified Diagnostic Services) is a diagnostic communication protocol in the electronic control unit (ECU) environment within the automotive electronics. 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. 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.

OBD (On-board diagnostics) is an automotive term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or repair technician access to the status of the various vehicle subsystems.
It is used to implement vehicle diagnostics communication for diagnosis and repair of vehicle sub-systems through communication with Electronic Control Units (ECU). ECUs monitor and control the sub-systems of a vehicle. Common ECUs include Engine Control Module (ECM), Transmission Control Module (TCM), Electronic Brake Control Module (EBCM), etc. Thus OBD helps to detect and control engine failures, performance issues and fight vehicle emission.
Generally, UDS and OBD are both diagnostic protocol, but they are actually not comparable. While UDS protocol is used to diagnose a fault in an off-board condition, i.e. when the car is at the service center, OBD is essentially an onboard diagnostic service.

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