SPN + FMI decoder
Decode a heavy-truck SPN and FMI: parameter name when we have verified it, generic FMI meaning, and a link to the full sheet when one is published.
How to read an SPN/FMI code
On a heavy truck, a fault is usually two numbers. The SPN (Suspect Parameter Number) names the signal the module is watching: oil pressure, outlet NOx, DEF tank level, and so on. The FMI (Failure Mode Identifier) says what looks wrong with that signal: voltage high, data erratic, value above the normal range.
Write both numbers down before you clear anything. SPN 3226 FMI 2 is not the same job as SPN 3226 FMI 3. The table under this tool is the generic FMI list from the shop manual we checked. It does not replace the engine maker’s troubleshooting tree, and it does not give you a pressure or temperature limit.
If this site has a full sheet for the SPN, open it. If the name is missing, the SPN is not in the short list we verified against those manuals. The FMI meaning can still be shown.
FMI 0–31 reference
Meanings for FMI 0–21 are the generic descriptions in Allied Systems manual 80-1287 (rev. 06-2019). FMI 22–31 are valid numbers; that manual does not define them, so this table leaves them blank.
| FMI | Generic meaning |
|---|---|
| 0 | Data valid but above normal operational range |
| 1 | Data valid but below normal operational range |
| 2 | Data erratic, intermittent, or incorrect |
| 3 | Voltage above normal or shorted high |
| 4 | Voltage below normal or shorted low |
| 5 | Current below normal or open circuit |
| 6 | Current above normal or grounded circuit |
| 7 | Mechanical system not responding properly |
| 8 | Abnormal frequency, pulse width, or pending |
| 9 | Abnormal update rate |
| 10 | Abnormal rate of change |
| 11 | Failure mode not identifiable |
| 12 | Bad intelligent device or component |
| 13 | Out of calibration |
| 14 | Special instructions |
| 15 | Data valid but above normal operating range - least severe level |
| 16 | Data valid but above normal operating range - moderately severe level |
| 17 | Data valid but below normal operating range - least severe level |
| 18 | Data valid but below normal operating range - moderately severe level |
| 19 | Received network data in error |
| 20 | Data drifted high |
| 21 | Data drifted low |
| 22 | Not defined in the validated sources. |
| 23 | Not defined in the validated sources. |
| 24 | Not defined in the validated sources. |
| 25 | Not defined in the validated sources. |
| 26 | Not defined in the validated sources. |
| 27 | Not defined in the validated sources. |
| 28 | Not defined in the validated sources. |
| 29 | Not defined in the validated sources. |
| 30 | Not defined in the validated sources. |
| 31 | Not defined in the validated sources. |