On Board Diagnostic¶

An On Board Diagnostic is an activity performed by the system itself as part of its functionality. Normally it is a support feature (except for the cases the OBD is diagnosticating external systems), and can be activated during part of the system’s (lifetime/working cycles/engineering-production stage) or during all of them.

An OBD can be described using a pattern algorithm that checks some conditions and raise some flags. If the OBD algorithm is universalized, then all the flags and conditions can be specified using a document (like HwSw_Interfaces). A software implementation of this algorithm makes it easier to universalize.

We can use the word “Fault” as a synonymous of OBD.

Normally, the OBD are grouped into OBD requirements. An OBD requirement is targetted to diagnosticate differented faults related to the same component of feature of the system (f.i. an OBD requirement can be “Battery Line OBDs” and some OBDs inside that group can be “Voltage Too Low”, “Voltage Too High”, etc...

On most implementations, the OBD activity produces the following results:

Name	Description	Required?
Test completed flag	At least one test for this OBD has been completed for this system work cycle
Fault present	The fault that OBD is trying to diagnosticate is currently present
Degradation flags	As the fault is present, OBD can also trigger some flags to help the system to react safely to this fault

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