What is SPN 3659 FMI 5 & How to Solve It?

What is SPN 3659 FMI 5:

SPN 3659 is associated with Aftertreatment 1 Diesel Particulate Filter (DPF) Regeneration Status, and FMI 5 means the circuit is open or current is below normal.

This fault signals an issue with the regeneration process wiring or signal, possibly interrupting or preventing proper DPF cleaning.

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Why This Happens

• Open circuit in regeneration control wiring.
• Faulty DPF temp or pressure sensor affecting regen trigger.
• ECM not receiving signal to initiate regen.
• Wiring harness damaged or disconnected.
• Fuse or relay fault in regen command circuit.

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How to Fix It

1. Inspect regen wiring harness and connectors for damage.
2. Test sensors involved in triggering regen (temp, pressure, etc.).
3. Check for blown fuses or failed relays.
4. Manually trigger a regen using diagnostics to confirm the circuit.
5. Repair or replace components and clear the fault code.

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How to Avoid It Before It Happens

1. Regularly test regen functionality during maintenance.
2. Keep sensor and actuator connectors clean and secured.
3. Replace weak relays or fuses during seasonal servicing.
4. Use test regens to confirm circuit health.