J1939-73 Diagnostic Message (DM1)


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Why with 2 or more alarms does DM1 stop broadcasting? I monitored with a CAN analizer, J1939 data, and I noted that with one alarm I receive CAN data correcly (18FECA00), but with 2 or more alarms this data stops broadcasting. Somebody know why the engine has this behaviour?

Thanks a lot,

When there is more then 1 alarm, it uses the multi packet protocol to send the alarms since for anything more then 1 alarm, the information will not fit in the DM1 message. I believe this is defined in J1939-21, and i'm going by memory but i think the telegrams are 1CEBFF00 and 1CECFF00. ECFF is an anouncing telegram, and then EBFF contains the actual data. one byte (the MSB i think) in each of the EBFF's is an index byte, and the remaining 7 contain the actual data.