How can I design Diagnostic Handler in my ECU?

Question

In my application, there is a requirement from our internal customer about diagnosis. After discussion a bit, We defined up to 20 Diagnosis cases which we will want to send to the target vehicle if required. But so far, We have never worked on diagnosis.

 I know there are some standards such as OBD or UDS but I could not find any paper about how diagnosis is managed in CAN.

What I understand about the Diagnostic System in Autosar is that if an error case occurs, ECU will store it to a specific address with specific ID. Then, If a diagnostic session start request comes from CAN, ECU will allow  to read diagnostic memory somehow.

Do these session requests only come from Diagnosis Tools ? If my ECU is broken, how could I inform the BUS ? If a bus is able to start a diagnostic session, does this happen periodically ? Are there any ways to handle this in a more simple way without touching UDS ?

Answer 1

Giving a basic training on diagnostic protocols, vehicle diagnostics and the AUTOSAR diagnostic stack in stack overflow is not realistic, but more a topic for a few weeks of coaching.

However, this is the short version:

• Theoretically you could use the "response on event" functionality, to inform a on- or off-board diagnostic client that a DTC changed state.
• Practically I never saw this for a use-case, where other ECU needed this information.
• Usually the vehicle defines periodic CAN signals, which are used to reports enough, that it can change its behavior if required.
• Then a summarized bit exists in a message, e.g. in something like a node message, which informs the vehicle whether any DTC is confirmed.

In an AUTOSAR application you would do the following:

• Your software components have client interfaces to the diagnostic event manager, to inform it about diagnostic events
• The diagnostic event manager maps them to DTCs and provided, together with the diagnostic communication manager, the transport protocol and other communication related modules, the interface for diagnostic clients to read this out.
• Another software component polls the status from the diagnostic event manager and sets a COM signal based on that information.