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
The reference is free. The diagnosis is Pro.
Every SPN and FMI page on this site stays open — no account needed. Pro members can take the code into Blue Collar AI with the VIN, symptoms and photos, keep per-truck history, and print a work order. $14.99 a month or $99.99 a year.