Unified Diagnostic Services (UDS) is a diagnostic
communication protocol
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics (computer scien ...
used in
electronic control unit
An electronic control unit (ECU), also known as an electronic control module (ECM), is an embedded system in automotive electronics that controls one or more of the electrical systems or subsystems in a car or other motor vehicle.
Modern vehic ...
s (ECUs) within automotive electronics, which is specified in the ISO 14229-1. It is derived from ISO 14230-3 (
KWP2000 Keyword Protocol 2000, abbreviated KWP2000, is a communications protocol used for on-board vehicle diagnostics systems (OBD). This protocol covers the application layer in the OSI model of computer networking. The protocol is standardized by Intern ...
) and the now obsolete
ISO 15765
ISO 15765-2, or ''ISO-TP (Transport Layer)'', is an international standard for sending data packets over a CAN-Bus. The protocol allows for the transport of messages that exceed the eight byte maximum payload of CAN frames. ISO-TP segments longe ...
-3 (Diagnostic Communication over
Controller Area Network
A Controller Area Network (CAN bus) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other's applications without a host computer. It is a message-based protocol, designed originally for mu ...
(DoCAN)
). '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
An original equipment manufacturer (OEM) is generally perceived as a company that produces non-aftermarket parts and equipment that may be marketed by another manufacturer. It is a common industry term recognized and used by many professional or ...
(OEM), and is incorporated into other standards, such as
AUTOSAR. The ECUs in modern vehicles control nearly all functions, including
electronic fuel injection
Manifold injection is a mixture formation system for internal combustion engines with external mixture formation. It is commonly used in engines with spark ignition that use petrol as fuel, such as the Otto engine, and the Wankel engine. In a mani ...
(EFI),
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 has UDS services enabled. In contrast to the
CAN bus
A Controller Area Network (CAN bus) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other's applications without a host computer. It is a message-based protocol, designed originally for mu ...
protocol, which only uses the first and second layers of the
OSI model
The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...
, UDS utilizes the fifth and seventh layers of the OSI model. The Service ID (SID) and the parameters associated with the services are contained in the payload of a message frame.gh
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 communication system of the vehicle. Thus, UDS requests can be sent to the controllers which must provide a response (this may be positive or negative). This makes it possible to
interrogate
Interrogation (also called questioning) is interviewing as commonly employed by law enforcement officers, military personnel, intelligence agencies, organized crime syndicates, and terrorist organizations with the goal of eliciting useful infor ...
the fault memory of the individual control units, to update them with new firmware, have low-level interaction with their hardware (e.g. to turn a specific output on or off), or to make use of special functions (referred to as routines) to attempt to understand the environment and operating conditions of an ECU to be able to
diagnose
Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine " cause and effect". In systems enginee ...
faulty or otherwise undesirable behavior.
Services
SID (Service Identifier)
See also
*
On-board diagnostics
On-board diagnostics (OBD) is a 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 sub-systems. The amount of diagnostic inf ...
, general article about diagnostic services in vehicles
*
OBD-II PIDs
OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool.
SAE standard J1979 defines many OBD-II PIDs. All on-road vehicles and trucks sold in North America are required to support a ...
, about the US standard
References
{{Reflist
External links
Unified Diagnostic Services - ISO 14229(poster by softing.com)
Automotive technologies
Embedded systems