SPN 4076 FMI 19Medium
DEF Doser Flow - Data Erratic
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 4076 / FMI 19
Severity
Medium
Regen Inhibit
No
Inducement Risk
No
Component Location: DEF doser injector is typically mounted on the exhaust pipe or DOC/DPF inlet mixing tube, downstream of the turbocharger, accessible from under the vehicle or cab.
Common Symptoms
- MIL/CEL illuminated. DEF warning lamp on. Erratic or fluctuating DEF dosing rate displayed on scan tool. Intermittent NOx efficiency faults (SPN 4094 or similar). Poor SCR conversion efficiency. DEF consumption may appear inconsistent — sometimes too high, sometimes too low. Possible ammonia smell from exhaust during erratic over-dosing events. Driver may report DEF gauge readings that don't match actual usage.
Root Causes
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Derate Behavior
Mileage / Regen Notes
This fault typically does not directly inhibit DPF active regeneration, as regen is primarily soot-load driven. However, if the erratic doser flow data causes the ACM to limit or halt DEF dosing, SCR inlet temperatures may be affected during regen events. Prolonged dosing issues can lead to elevated NOx and secondary codes that may eventually inhibit regen. Monitor for related SCR efficiency faults which can trigger regen lockout.
System Interactions
SPN 4076 FMI 19 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: No confirmed universal TSBs — verify in OEM service portal. Cummins, Detroit, and Paccar have released bulletins on DEF doser harness routing and connector sealing issues; search by SPN 4076 in OEM system. Some OEMs have issued reflash updates for ACM calibration related to erratic dosing signal interpretation.
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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4076 FMI 19 — 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.
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.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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