What is SPN 5246 FMI 15 (Caterpillar) & How to Solve It?

What is SPN 5246 FMI 15 (CAT):

On Caterpillar engines, SPN 5246 FMI 15 is a DEF-related inducement code, meaning the system is about to limit performance due to excessive or unresolved aftertreatment faults.

It’s triggered when the engine control system detects serious DEF dosing or sensor problems, and the machine is at risk of entering full derate.

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Why This Happens

• DEF quality, level, or dosing faults not resolved.
• Failed or bypassed regeneration events.
• Exhaust or aftertreatment sensors out of range.
• DEF pump failure or poor pressure.
• Tampering or ECM misconfiguration.

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How to Fix It

1. Identify and resolve all active emissions-related codes.
2. Refill DEF with fresh, certified fluid.
3. Check pump, sensor, and tank module performance.
4. Perform a forced regen to reset DPF and SCR status.
5. Clear all faults and confirm engine exits inducement mode.

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How to Avoid It Before It Happens

1. Address DEF warnings immediately — don’t wait.
2. Keep fluid clean, stored correctly, and sealed.
3. Replace worn-out sensors before they start failing.
4. Educate operators on completing regens properly.

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