FMI 31 — Condition exists
A general 'this state is true' flag. It is not a circuit failure — the ECM is reporting that a defined condition is active, such as a regen inhibited or a switch in a given position.
Common causes
- A monitored condition became true (inhibit active, switch set, mode entered)
- Related system fault causing the condition
- Operator input or configuration
What to test, in order
- Read the SPN description to identify which condition is being reported
- Check for other active codes that would cause it
- Verify switch and operator inputs in live data
- Clear it, run the truck and see whether it returns
Codes we document with FMI 31
SPN 3936 FMI 31Aftertreatment system incomplete regeneration · PACCARSPN 4094 FMI 31NOx conversion inducement - severe derate active · CATSPN 4094 FMI 31NOx conversion inducement - severe derate active · DetroitSPN 4094 FMI 31NOx conversion inducement - severe derate active · InternationalSPN 4094 FMI 31NOx conversion inducement - severe derate active · PACCARSPN 4094 FMI 31NOx conversion inducement - severe derate active · MERCEDESSPN 4094 FMI 31NOx conversion inducement - severe derate active · VolvoSPN 4094 FMI 31NOx conversion inducement - severe derate active · MackSPN 4094 FMI 31NOx conversion inducement - severe derate active · Cummins
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