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Fault Code Reference

SPN 1807 FMI 1AftertreatmentInducement Risk

Aftertreatment Fuel Pressure - Data Valid But Below Normal

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Overview

Fault Code

SPN 1807 / FMI 1

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: Aftertreatment fuel dosing unit and pressure sensor are typically mounted on or near the DPF/DOC assembly under the cab or along the frame rail.

Common Symptoms

  • DPF regeneration fails to initiate or complete
  • Dosing malfunction indicator lamp illuminated
  • Insufficient DEF/diesel injection into exhaust stream
  • White smoke from exhaust during regen attempt
  • Low aftertreatment fuel pressure code
  • Poor DEF dosing performance

Root Causes

  • Clogged or restricted aftertreatment fuel supply line or filter Failed or weak aftertreatment dosing pump (insufficient pressure output) Aftertreatment fuel shutoff valve stuck closed or partially blocked Air in the aftertreatment fuel supply system causing pressure drop Low engine fuel pressure feeding the aftertreatment fuel circuit Faulty aftertreatment fuel pressure sensor giving low reading Cracked, kinked, or collapsed aftertreatment fuel supply hose Aftertreatment fuel filter plugged with debris or wax (cold weather) Leaking fuel line fitting upstream of dosing unit causing pressure loss ACM calibration or software issue misreading pressure signal

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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; dosing of fuel into the aftertreatment system is disabled to prevent uncontrolled regeneration or injector damage. Vehicle may enter a derate condition if fault is persistent.

System Interactions

SPN 1807 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.

Deep-dive diagnostic page: SPN 1807 FMI 1 — 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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