Variable PGN_DM1Const

J1939 Diagnostics Module (DM)

DM1: Active Diagnostic Trouble Codes

• Byte 0: Lamp status and flash codes
• Bytes 1-7: Up to 3 DTCs (each DTC = 4 bytes: SPN + FMI)

DM2: Previously Active DTCs (same structure as DM1)

DM format:

• Bytes 0: Malfunction Indicator Lamp (MIL) + other lamps
• Bytes 1-7: DTC data (SPN = bytes 1-3, FMI = byte 4)