FMI Codes: Common Meanings and Scope
What the FMI identifies
The Failure Mode Identifier describes the reported failure mode. Use it with the SPN and reporting controller. An electrical label, a calibration label and a performance label lead to different questions; none is a replacement instruction by itself.
Common meanings and reference limits
This table summarizes familiar FMI meanings found in OEM fault lists and the legacy diagnostic reference below. It is not a complete current SAE Appendix A. Values 22–30 are deliberately left undefined here: consult the applicable J1939-73 edition rather than assuming all are reserved or manufacturer-assigned. SAE J1939-73 — Application Layer: Diagnostics · FCAR Tech USA — FMI reference
| FMI | Meaning summary |
|---|---|
| 0 | Valid high reading; greatest severity |
| 1 | Valid low reading; greatest severity |
| 2 | Erratic, intermittent or incorrect data |
| 3 | High voltage or short to a high source |
| 4 | Low voltage or short to a low source |
| 5 | Low current or open circuit |
| 6 | High current or grounded circuit |
| 7 | Mechanical response or adjustment problem |
| 8 | Frequency, pulse width or period outside expectations |
| 9 | Unexpected update timing |
| 10 | Unexpected rate of change |
| 11 | Root cause unidentified |
| 12 | Intelligent device/component fault |
| 13 | Calibration outside requirements |
| 14 | Follow special instructions |
| 15 | Valid high reading; least severity |
| 16 | Valid high reading; moderate severity |
| 17 | Valid low reading; least severity |
| 18 | Valid low reading; moderate severity |
| 19 | Received network data indicates an error |
| 20 | Upward data drift |
| 21 | Downward data drift |
| 22–30 | Revision-specific assignments: not defined in this guide |
| 31 | The named condition is present |
Use the complete code and application
For example, the Cummins cross-reference distinguishes outlet NOx 3226/FMI 9 from inlet NOx 3216/FMI 9. The update-rate meaning does not make those the same sensor. Cummins SPN/FMI cross-reference — Atlas Copco
Read the OEM fault title, prerequisites and wiring diagram before using a test. Do not assign every generic FMI to every SPN: the individual guides list documented combinations with their application and source. Where an OEM title uses different terminology, preserve the actual numeric code and follow the matching procedure.
Sources and applicability
Source check: September 12, 2026. These are documented examples. Confirm the engine serial number, software calibration and current OEM instructions before using a test or repair procedure.
- SAE J1939-73 — Application Layer: Diagnostics — Standards reference. The full current Appendix A is not reproduced or certified by this guide; use the edition required for the vehicle.
- FCAR Tech USA — FMI reference — Legacy diagnostic-tool reference, cross-checked against OEM code tables; not evidence of current assignments for every value from 22 to 30.
- Cummins SPN/FMI cross-reference — Atlas Copco — 2013 ISX15, ISX12, ISL9 and ISB6.7; use only the applications marked in the source table.
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