SPN 3360 FMI 9AftertreatmentMedium
DEF Doser - Update Rate Abnormal (CAN Fault)
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 3360 / FMI 9
Category
Aftertreatment
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: DEF doser is mounted on the decomposition tube or mixer assembly upstream of the SCR catalyst in the exhaust system.
Common Symptoms
- MIL/CEL illuminated, DEF warning lamp on, no DEF injection or erratic dosing, possible white smoke during dosing attempts, DEF level gauge may read incorrectly, other aftertreatment-related fault codes present (SCR efficiency codes), poor NOx conversion, ammonia smell from exhaust if doser stuck open, communication lost message on scan tool for DEF doser module
Root Causes
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
Active regeneration may be inhibited while this fault is active. Without reliable DEF doser communication, the ACM cannot confirm proper dosing for SCR operation, which may prevent the system from initiating or completing active regen. Parked regen will likely be blocked as well. SCR inlet temps and dosing verification depend on doser feedback. Resolve CAN communication before attempting forced regen.
System Interactions
SPN 3360 FMI 9 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. Cummins ISB/ISX: check for bulletins on aftertreatment harness routing and connector sealing. Detroit DD13/DD15: check for CAN wiring service campaigns near DEF tank and doser. Paccar MX: review TSBs related to aftertreatment harness chafing. Always search by SPN 3360 in OEM system.
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 3360 FMI 9 — 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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