Unified Diagnostic Services

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. It is derived from ISO 14230-3 (KWP2000) and ISO 15765-3 (Diagnostic Communication over Controller Area Network (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 almost all new ECU software projects of vehicle manufacturers such as electronic fuel injection (EFI), automatic gear box, anti-lock braking system, Configurable Engine Mobilizer, Key Controls, Wiper Controls etc.

The diagnostics services able to contact all control units installed in a vehicle, which is using UDS. In contrary to the CAN protocol, which only the first and second layer of the OSI model, the UDS service itself uses the fifth and seventh layers of the OSI model. Modern vehicles have a diagnostic interface for off-board diagnostics, which makes it possible to connect a computer (client), 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.

SID (Service Identifier)

In addition, there are reserved session identifiers that can be defined for vehicle manufacturers and vehicle suppliers specific use.

Again, there are reserved values that can be defined for vehicle manufacturers and vehicle suppliers specific use.

The requested data may be configured or grouped in the following manner:

By specifying a so-called option bytes additional conditions for a request can be specified, the following values are specified:

ReturnControlToECU: The device must get back controls of the mentioned signals.

ResetToDefault: The tester prompts to reset signals to the system wide default value.

Freeze Current State: The device shall freeze the current signal value.

ShortTermAdjustment: The device shall use the provided value for the signal

The start and stop message parameters can be specified. This makes it possible to implement every possible project-specific service.

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