SPN 4761 FMI 5AftertreatmentInducement Risk
Aftertreatment 1 DEF Doser 1 - Current Below Normal
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Overview
Fault Code
SPN 4761 / FMI 5
Category
Aftertreatment
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: DEF doser injector is mounted on the DEF decomposition tube or mixing pipe, downstream of the DPF and upstream of the SCR catalyst, typically mid-chassis or under the cab.
Common Symptoms
- Check engine light illuminated
- DEF system malfunction warning
- Engine derate or power reduction
- DEF dosing system inactive
- Poor NOx conversion efficiency
- Possible inducement warning messages
Root Causes
- Open circuit in DEF doser supply or return wiring harness Corroded or damaged DEF doser electrical connector Failed DEF doser injector (open coil winding) Blown fuse in DEF doser supply circuit Broken or chafed wire between ACM and DEF doser Poor ground connection at DEF doser or ACM Failed ACM output driver for DEF doser circuit Connector pin pushed back or not fully seated at ACM harness
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Derate Behavior
Power Derate
Yes
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
SPN 4761 FMI 5 (DEF doser current below normal) will typically inhibit active DEF dosing into the SCR system. Without dosing, NOx conversion is lost and the ACM may inhibit or abort parked and active DPF regeneration events. Extended fault presence can trigger SCR derating or engine derate depending on OEM threshold timers.
System Interactions
SPN 4761 FMI 5 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
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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4761 FMI 5 — 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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