What are the symptoms of SPN 3700 FMI 1?

Doser fuel pressure below normal operating range. Insufficient DEF/doser fuel delivery. Failed or incomplete regenerations. Aftertreatment system malfunction lamp illuminated. Poor NOx conversion efficiency. DPF regeneration failure or abort

What causes SPN 3700 FMI 1?

Clogged or restricted aftertreatment fuel supply line or filter Faulty or worn aftertreatment fuel dosing pump (7th injector pump) with low output pressure Air in the aftertreatment fuel supply system causing pressure drop Leaking or damaged aftertreatment fuel pressure sensor giving low reading Restricted aftertreatment fuel inlet strainer/screen Low main fuel tank level causing insufficient fuel supply to dosing system Failed or weak aftertreatment fuel shutoff valve not opening fully Wiring or connector issue causing erroneous low pressure signal to ACM

How do I diagnose SPN 3700 FMI 1?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 3700 FMI 1 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 3700 FMI 1AftertreatmentInducement Risk

Aftertreatment Fuel Pressure - Data Valid But Below Normal

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Overview

Fault Code

SPN 3700 / FMI 1

Common Symptoms

Doser fuel pressure below normal operating range
Insufficient DEF/doser fuel delivery
Failed or incomplete regenerations
Aftertreatment system malfunction lamp illuminated
Poor NOx conversion efficiency
DPF regeneration failure or abort

Root Causes

Clogged or restricted aftertreatment fuel supply line or filter Faulty or worn aftertreatment fuel dosing pump (7th injector pump) with low output pressure Air in the aftertreatment fuel supply system causing pressure drop Leaking or damaged aftertreatment fuel pressure sensor giving low reading Restricted aftertreatment fuel inlet strainer/screen Low main fuel tank level causing insufficient fuel supply to dosing system Failed or weak aftertreatment fuel shutoff valve not opening fully Wiring or connector issue causing erroneous low pressure signal to ACM

Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.

AI walks you through every test — one step at a time. Plans start at $12.95/mo.

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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

Active and parked DPF regeneration will be inhibited when aftertreatment fuel pressure is below normal, as the ACM cannot command a safe dosing event. The system may suspend all regen attempts and illuminate the DPF warning lamp until pressure is restored within spec.

System Interactions

SPN 3700 FMI 1 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

SPN 5246-31SCR NOx Efficiency Low SPN 4364-18DEF Dosing Below Normal SPN 3364-2DEF Quality Erratic SPN 3251-0DPF Differential Pressure High SPN 3719-16DPF Soot Load High

OEM System Resources

Cummins Fault Codes Detroit Diesel Fault Codes PACCAR Fault Codes Volvo Fault Codes Freightliner Fault Codes Mack Fault Codes

ASE Training Resources

Why ASE Certification Matters How ASE Tests Work ASE Study Tips ASE vs AI Diesel Tech Certification Paths Get Started with ASE

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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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