Template:FMX6 DM1 DM2: Difference between revisions
Updating per GTPGTM-11768 |
Updating per GTPGTM-11768 - 3 new paragraphs added and existing ones updated or reworded |
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With {{{model}}} you can read 2 types of DTC messages based on J1939 protocol: | With {{{model}}} you can read 2 types of DTC messages based on J1939 protocol: | ||
*DM1 – | *DM1 – Communicates currently present faults | ||
*DM2 – | *DM2 – Reports stored faults | ||
{{{model}}} is able to read DM codes and pass them to the server in IO element. When active DM1 | {{{model}}} is able to read DM codes and pass them to the server in IO element. When active DM1 messages are present on the CAN line, they are broadcast frequently. The {{{model}}} device stores these codes in its internal memory and transmits only newly detected DTC codes. | ||
DM2 messages are not streamed, but instead, they must be requested. | |||
==Functionality Description== | ==Functionality Description== | ||
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'''39443030303330313A30313A30313B''' -> (after conversion from hex to ANSCII) '''9D000301:01:01'''; | '''39443030303330313A30313A30313B''' -> (after conversion from hex to ANSCII) '''9D000301:01:01'''; | ||
[[File: | ==DM1/DM2 Message Structure== | ||
'''DM1''' is a J1939 diagnostic message used to broadcast active faults and warning lamp status. Its structure is split into a header (lamp status) followed by one or more diagnostic trouble codes. Unlike most J1939 messages, DM1 has a variable length: if there are 0–1 active DTCs, it fits in a single CAN frame, while 2 or more DTCs require a multi-frame message with additional DTC entries added. | |||
[[File:DM1 and DM2 Message Structure.png]] | |||
The first 2 bytes form the lamp status header, which is shared across all DTCs. Each lamp uses 2-bit values to indicate status (off/on), along with flash signals defining how the lamp blinks (slow or fast). These signals are interpreted collectively across ECUs, with a central controller typically deciding the final lamp behavior based on the most severe reported condition. | |||
Each DTC contains four key components: | |||
*'''SPN(''Suspect Parameter Number)''''' - Identifies the faulty subsystem. | |||
*'''FMI(''Failure Mode Identifier)''''' - Describes the type of failure. | |||
*'''CM(''SPN Conversion Method)''''' - Indicates the encoding method. | |||
*'''OC(''Occurrence Count)''''' - Counts how often the fault has occurred. | |||
These elements provide detailed, structured information about vehicle faults while supporting both standardized and proprietary diagnostics. | |||
==DM1 Lamp Status and Flash Signals== | ==DM1 Lamp Status and Flash Signals== | ||
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The SPNs for proprietary codes typically occupy the high end of the 19-bit field, ranging from '''516,096 to 524,287'''. FMI values may be standard or custom, but the meaning of the SPN is defined by the manufacturer. Accurate interpretation requires access to OEM documentation, as these codes are not universally defined or interpretable. | The SPNs for proprietary codes typically occupy the high end of the 19-bit field, ranging from '''516,096 to 524,287'''. FMI values may be standard or custom, but the meaning of the SPN is defined by the manufacturer. Accurate interpretation requires access to OEM documentation, as these codes are not universally defined or interpretable. | ||
==DM1 | ==Functionality Block Diagram== | ||
Graphic representation of '''DM1''' and '''DM2''' functionality: | |||
[[File:DTC Functionality blok diagram.png]] | |||
[[File: | |||