What This FMI Means
FMI 25 is a failure-mode part of a J1939 diagnostic message. It does not identify the component by itself; it describes the type of condition reported for the SPN.
How It Appears With SPN Codes
A complete code such as SPN 1234 FMI 25 should be read as the parameter first and the failure mode second. The source address can help identify which module reported the condition.
What Drivers Should Record
Record the full SPN/FMI, active or inactive status, warning lamps, derate status, mileage or engine hours, and any related codes before clearing or changing anything.
Why OEM Diagnosis Still Matters
The same FMI can appear across different systems. OEM diagnostic software and service information are needed for final diagnosis because wiring, calibration, operating state, and related module data all matter.
Related Pages
Sources
- SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Does FMI 25 identify the failed part?
No. It describes the failure mode. The SPN, module, related codes, and OEM information are needed before drawing conclusions.
Can FMI 25 appear on different truck systems?
Yes. FMI values are reused across many SPNs and systems, so context is essential.
Should I clear an SPN/FMI 25 code first?
Record the full code and related conditions first. Clearing codes before documentation can remove useful diagnostic context.