Unified Diagnostic Services


Unified Diagnostic Services is a diagnostic communication protocol used in electronic control units within automotive electronics, which is specified in the ISO 14229-1. It is derived from ISO 14230-3 and the now obsolete ISO 15765-3. 'Unified' in this context means that it is an international and not a company-specific standard. By now this communication protocol is used in all new ECUs made by Tier 1 suppliers of Original Equipment Manufacturer, and is incorporated into other standards, such as AUTOSAR. The ECUs in modern vehicles control nearly all functions, including electronic fuel injection, engine control, the transmission, anti-lock braking system, door locks, braking, window operation, and more.
Diagnostic tools are able to contact all ECUs installed in a vehicle, which have UDS services enabled. In contrast to the CAN bus protocol, which only uses the first and second layers of the OSI model, UDS utilizes the fifth and seventh layers of the OSI model. The Service ID and the parameters associated with the services are contained in the 8 data bytes of a message frame.
Modern vehicles have a diagnostic interface for off-board diagnostics, which makes it possible to connect a computer or diagnostics tool, which is referred to as tester, to the communication system of the vehicle. Thus, UDS requests can be sent to the controllers which must provide a response. This makes it possible to interrogate the fault memory of the individual control units, to update them with a new firmware, have low-level interaction with their hardware, or to make use of special functions to attempt to understand the environment an operating conditions of an ECU to be able to diagnose faulty or otherwise undesirable behaviour.

Services

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