Unified Diagnostic Services (UDS) is a diagnostic communication protocol in the electronic control unit (ECU) environment within the automotive electronics, which is specified in the ISO 14229-1.[1] It is derived from ISO 14230-3 (KWP2000) and ISO 15765-3 (Diagnostic Communication over Controller Area Network (DoCAN)[2]). Unified in this context means that it is an international and not a company-specific standard. By now this communication protocol is used in almost all new ECUs made by Tier 1 suppliers of Original Equipment Manufacturer (OEM). These ECUs control a wide range of functions in vehicles including electronic fuel injection (EFI), engine control, the transmission, anti-lock braking system, door locks, braking, and more.

The diagnostic tool contacts all control units installed in a vehicle, which have UDS services enabled. In contrast to the CAN protocol, which only uses the first and second layers of the OSI model, UDS services utilize the fifth and seventh layers of the OSI model. The Service ID (SID) and the parameters associated with the services are contained in the 8 data bytes of a message frame issued from the diagnostic tool.

Modern vehicles have a diagnostic interface for off-board diagnostics, which makes it possible to connect a computer (client) or diagnostics tool, which is referred to as tester, to the bus system of the vehicle. Thus, the messages defined in UDS can be sent to the controllers which must provide the predetermined UDS services. This makes it possible to interrogate the fault memory of the individual control units or to update them with a new firmware.

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