Truck Fault Codes

FMI 31 Explained

FMI 31 generally means the condition is not available or is defined by the reporting system. The final interpretation depends on the SPN, source address, OEM calibration, active status, and related codes.

Review status: source-backed medium Last reviewed: 2026-04-14

What This FMI Means

FMI 31 means the reported condition exists — the SPN identifies what the condition is; FMI 31 confirms it is active. This FMI is used when the ECM is reporting a specific operational state or protective event rather than a circuit fault or measurement threshold exceedance. The module is not describing a broken wire or sensor drift — it is describing a confirmed system state.

FMI 31 codes are common in aftertreatment systems (inducements active, regeneration required), engine protection systems (derate active), and OEM-defined operational states such as specific operating mode limits. The SPN defines the specific condition; FMI 31 confirms it is currently present.

How It Appears With SPN Codes

SPN 5246 FMI 31 is one of the most frequently encountered FMI 31 combinations — it indicates an SCR aftertreatment inducement is active, typically triggered by DEF level below threshold, DEF quality failure, or NOx conversion efficiency below the required threshold. SPN 3936 FMI 31 indicates a DEF dosing inducement. SPN 1569 FMI 31 indicates engine protection torque derate is active.

These FMI 31 codes are consequences of underlying faults — DEF system problems, NOx sensor failures, or aftertreatment degradation — and represent the ECM's protective response to those conditions. The underlying fault codes (DEF level, DEF quality, NOx sensor) are the primary faults; FMI 31 on the inducement SPN is the triggered state.

How to Approach Diagnosis

Look for related fault codes alongside FMI 31 — the underlying cause of the FMI 31 state is almost always visible in the fault log. FMI 31 on SPN 5246 (SCR inducement) typically co-occurs with DEF level, DEF quality, or NOx efficiency fault codes. Address the underlying fault first; the FMI 31 condition should resolve once the cause is corrected.

Clearing FMI 31 codes without addressing the underlying condition will result in their return. For aftertreatment inducements, the inducement counter must also be reset using OEM diagnostic software (Cummins Insite, Detroit DiagnosticLink, or Volvo/Mack tech tool) after the underlying fault is corrected. Clearing the fault code alone does not reset an inducement counter that has crossed a threshold — the reset procedure is separate.

What Drivers Should Record

Record all active codes — not just the FMI 31 codes — because the related codes identify the specific system fault causing the FMI 31 state. Record DEF level reading, DEF brand and batch if available, the last successful DPF regen date or mileage if shown in the instrument cluster, and any operational events such as missed regens or extended idling.

Note the current derate level if one is active. SCR inducement derates on Cummins, Detroit, and Volvo/Mack engines are progressive — crossing the first threshold triggers a moderate power reduction while subsequent thresholds apply more severe restrictions up to a very limited idle-only operation. The current derate level indicates how advanced the condition is and helps the service team assess urgency.

Related Pages

Related Fault Code 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
  • NHTSA Manufacturer Communications Search National Highway Traffic Safety Administration · government · accessed 2026-05-05 · confidence high

    Source: National Highway Traffic Safety Administration, NHTSA Manufacturer Communications Search. This page paraphrases factual fields only and is not a substitute for the original document.

    Open source

FAQ

FMI 31 says 'condition exists' — what condition, exactly?

FMI 31 is used when the ECM is reporting a specific state or event that doesn't fit a more descriptive FMI category. The SPN tells you what is being reported; FMI 31 simply confirms the condition is present. Examples include aftertreatment inducement active (SPN 5246 FMI 31), specific engine protection events, and OEM-defined states. The SPN is the critical identifier — FMI 31 adds that the condition is confirmed active.

Is FMI 31 more serious than FMI 1 or FMI 0?

Severity depends entirely on the SPN, not the FMI number. SPN 5246 FMI 31 (SCR inducement active on Cummins) is a significant derate condition. SPN 1569 FMI 31 (engine protection torque derate) is also serious. Other SPN/FMI 31 combinations may be lower priority. FMI 31 is not inherently more or less severe than other FMIs — it simply describes a confirmed state rather than a circuit fault or threshold exceedance.

If I clear a code with FMI 31, will it come back if the condition is still present?

Yes. FMI 31 codes that represent active operational states (like an inducement or a protection event) will return immediately or the next time the condition is confirmed. For an aftertreatment inducement with FMI 31, clearing the code does not reset the inducement counter — that requires OEM service software. For other FMI 31 condition-exists codes, the code will return if the triggering condition is still present.