SPN 4765 FMI 18AftertreatmentHighInducement Risk
Aftertreatment DEF Dosing Quantity — Below Normal
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 4765 / FMI 18
Category
Aftertreatment
Fault Type
actuator
FMI Category
electrical low
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: DEF dosing injector — in exhaust pipe upstream of SCR. DEF pump on frame rail.
Common Symptoms
- DEF dosing below commanded quantity
- SCR efficiency fault active
- NOx emissions high
- Possible inducement warning
Root Causes
- DEF injector partially clogged
- DEF pump not building full pressure
- DEF supply line restriction
- DEF injector solenoid weak
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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
Injector clogging common 200k–400k miles. Pump failures more common after 500k.
System Interactions
SPN 4765 FMI 18 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: Cummins TSB 4021543 — DEF Dosing Quantity Diagnosis
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.
OEM Notes
Cummins
ISX15: INSITE Dosing Quantity Test. Injector cleaning procedure available.
Detroit
DD15: DDDL Dosing Test. Check pump module pressure first.
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OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4765 FMI 18 — 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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