Transmits active Diagnostic Trouble Codes (DTCs).
While secondary sources and forum posts exist, relying on the authentic is non-negotiable for serious engineers and technicians. Sae J1939-73 Pdf
A 5-bit number describing the type of failure observed (e.g., FMI 3 means voltage above normal, FMI 4 means voltage below normal). Transmits active Diagnostic Trouble Codes (DTCs)
Used by service tools to command the ECU to clear active or previously active DTCs. FMI 3 means voltage above normal