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J1939 DTC Nomenclature
SA - Source Address
The SA field contains the ECU that is sending the message
Example: SA 0 = Engine
SA 3 = Transmission
SA 11 = Brakes System Controller
SPN - Suspect Parameter Number
The SPN is used to identify the item for which diagnostics are being reported
Example: SPN 156 = Injector Timing Rail 1 Pressure
SPN 031 = Transmission Range Position
SPN 639 = J1939 Network
FMI - Failure Mode Identifier
The FMI describes the type of failure detected in the part identified by the SPN. The FMI, and either the SPN
combined to form a given diagnostic Fault code.
Example: FMI 002 = Data erratic, Intermittent or incorrect
FMI 005 = Current below normal or Open circuit
FMI 007 = Mechanical System Not Responding
FMI 011 = Failure Mode not Identifiable
Normal Message
SA/SPN/FMI
or
3-639-02
03 = Transmission
639 = J1939
002 = Data erratic, Intermittent or incorrect
Example: The Transmission has detected the J1939
network has an error.
800.MACTOOLS
59
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