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Diagnostic Event Manager (DEM)

As per AUTOSAR specification "DEM handles and stores the events, detected by the Software Components using a Monitor Function above the RTE. The stored event information is available via an interface to other Basic software modules and Software Components". 

To put it in more simple words, Monitors(code parts which are written to detect faults in functionality) will report faults to DEM.DEM also collects and handles freeze frame data ( information like temperature, timestamp, mileage, etc..), so that this could be used in a service station to understand at what circumstance the fault occurred, thereby aiding to debug the fault

Architecture: SW-Cs report faults to DEM via service ports and DEM gets the freeze frame information from other SW-Cs. DEM communicates with NVM to read and write fault information and event data to NV memory and communicates with DCM to send data to the tester (eg. UDS service 19)

DEM Events: A Fault is called as a DEM event. To be more accurate, a ´Diagnostic Event´ defines the atomic unit that can be handled by the DEM module. Each DEM event is given an ID called eventID to uniquely identify it and also an Event name 

DEM event can have the following attributes

  • Diagnostic Trouble Code - DTC(s)  
  • Event priority (Every event will have priority, one use-case for this is where cascaded faults could be suppressed, for eg. if car has an Undervoltage error, the headlights might not function. So only Undervoltage should be reported not the headlight error because solving Undervoltage automatically will make the headlights work  )
  • Healing cycles (No. of driving cycles the fault should not reappear to stop the malfunction indicator lamp)
  • Healing allowed
  • Identification of the destination of an event 
  • Emission relevance (OBD fault definition)


Below are some important DEM APIs and their definitions taken from the AUTOSAR specification

Dem_Init The function Dem_Init is used during the startup phase of the ECU after the NVRAM manager has finished the restore of NVRAM data. SW-Components including Monitor Functions are initialized afterwards. The function Dem_Init is also used to reinitialize the DEM module after the Dem_Shutdown was called

Dem_Shutdown: Once this function has been executed, no further updates are applied to the DEM module internal event data

Dem_SetEventStatus: The function Dem_SetEventStatus will be called by a Monitor Function and it will store the diagnostic event (fault) and event-related data (Freeze Frame) to the Event Memory.

Dem_ResetEventStatus : The function Dem_ResetEventStatus will reset the Event Status stored in the Event Memory in the DEM module and is called by the monitor function when the fault is cleared.

Dem_GetEventStatus: The function Dem_GetEventStatus is used by FIM(typically FIM is the main user of this function) or other modules to read the event status from the DEM module for a specific event

Dem_ReportErrorStatus: This API has the same functionality as to Dem_SetEventStatus but this is used by BSW SW-Cs

To be continued...


  1. Hi Shankara,
    Thank you for providing insights of Autosar DEM. I just want a bit clarification on "Healing Cycle". As per as I know deletion of fault is related to Aging Cycle not Healing Cycle.
    Healing cycle is the number of cycles in which fault is not reported to make indicator off.
    Please provide your inputs.

    Thank you,

  2. Hi Namit,

    Ya,you are right.I have updated the description now.
    Thanks for pointing out


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