SPN 4766 FMI 0Aftertreatment
Aftertreatment Diesel Particulate Filter Regeneration Status - Data Valid But Above Normal
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Overview
Fault Code
SPN 4766 / FMI 0
Category
Aftertreatment
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: DPF is mounted in the exhaust system downstream of the turbocharger and DOC.
Common Symptoms
- Active regeneration occurring more frequently than normal
- Elevated exhaust temperatures during and after regen cycles
- Reduced fuel economy due to excessive regen frequency
- DPF soot load or ash load warnings active
- MIL or amber warning lamp illuminated
- Possible derate or power reduction in severe cases
- Driver notification of high regen status on dash display
Root Causes
- Excessive soot accumulation in DPF due to short-haul or low-load duty cycles Faulty or clogged DPF differential pressure sensor causing incorrect soot load calculation Plugged or damaged DPF requiring forced regen or replacement Malfunctioning DOC (Diesel Oxidation Catalyst) reducing regen efficiency Incorrect fuel injection quantity causing incomplete combustion and high soot output Faulty exhaust temperature sensors providing incorrect data to ECM EGR system malfunction increasing soot production High ash accumulation in DPF requiring service cleaning or replacement Air intake restriction causing rich combustion and elevated soot output Poor quality or incorrect specification diesel fuel
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
SPN 4766 FMI 0 indicates regen status is above normal operational range. Active regen may be triggered continuously or inhibited if DPF reaches critical soot threshold. Prolonged above-normal status can escalate to DPF protection derate, inhibiting vehicle speed or engine power until regen completes or DPF is serviced.
System Interactions
SPN 4766 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
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 4766 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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