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Fault Code Reference

SPN 3250 FMI 0AftertreatmentHighRegen InhibitInducement Risk

DOC Outlet Temperature - Very High

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Overview

Fault Code

SPN 3250 / FMI 0

Category

Aftertreatment

Severity

High

Derate Risk

Yes

Regen Inhibit

Yes — active regen blocked

Inducement Risk

Yes — SCR inducement possible

Component Location: DOC outlet temperature sensor is located in the exhaust system between the diesel oxidation catalyst and the DPF.

Common Symptoms

  • MIL/CEL illuminated with high exhaust temp warning. Noticeable power derate, especially under load. Possible limp mode activation. High temp reading on dash display or scan tool (DOC outlet exceeding 700°C+). Audible turbo surge or rough running during active regen. Strong diesel smell from exhaust due to excess fuel. Possible visible smoke (white or light gray) during regen events. Driver complaints of reduced speed and throttle response. Aftertreatment warning lamp on.

Root Causes

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Derate Behavior

Power Derate

Yes

Active Regen Inhibited

This fault prevents the DPF from completing an active regeneration cycle. DPF soot load will increase until the fault is resolved.

SCR Inducement Risk

If left unresolved, this fault may trigger SCR inducement — a progressive derate enforced by the ECM to ensure emissions compliance.

Mileage / Regen Notes

This fault will immediately INHIBIT active regeneration to prevent further thermal damage to the aftertreatment system. The ECM/ACM will not command dosing fuel until the fault is cleared and temps return to normal range. Parked regen will also be disabled. If the vehicle was in an active regen when the fault set, regen will abort immediately. The DPF will continue to accumulate soot with regens inhibited - extended operation without repair will lead to a severely plugged DPF requiring removal and cleaning or replacement. Manual regen attempts via scan tool will be blocked until the fault is addressed.

System Interactions

SPN 3250 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.

DPF differential pressure monitoring — soot load calculations affected
SCR NOx conversion efficiency — DEF dosing strategy may be altered
Active regen inhibit logic — regen may be blocked or delayed
Engine protection derate — ECM may reduce power to protect components
TSB Reference: No confirmed universal TSBs — verify in OEM service portal. Check Cummins QuickServe for ISB/ISX/ISL aftertreatment bulletins. Detroit Diesel may have relevant bulletins for DD13/DD15 dosing system calibration updates. Paccar has issued updates for MX-13 regen fuel control. Always search by engine serial number for applicable campaigns or service letters related to DOC over-temperature conditions or dosing valve updates.

Common Diagnostic Mistakes

Replacing the sensor without verifying wiring continuity and supply voltage first.

Clearing codes without identifying and resolving the root cause — the fault will return.

Ignoring related active faults — cascading faults often share a root cause.

Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.

Condemning the ECM before exhausting all wiring and component tests.

Replacing the DPF without verifying the regen system is functional — a failed regen injector will reload the new DPF.

Ignoring DEF quality — contaminated DEF causes SCR efficiency faults that look like hardware failures.

Deep-dive diagnostic page: SPN 3250 FMI 0 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.

Authority References

Diagnostic procedures on this page are informed by OEM service literature and industry standards.

EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.

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