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Fault Code Reference

SPN 4766 FMI 5Aftertreatment

Aftertreatment 1 Fuel Pressure Control Valve - Current Below Normal or Open Circuit

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Overview

Fault Code

SPN 4766 / FMI 5

Category

Aftertreatment

Derate Risk

No

Regen Inhibit

No

Inducement Risk

No

Component Location: The aftertreatment fuel pressure control valve is mounted on or near the aftertreatment fuel supply module, typically on the aftertreatment system assembly under the vehicle frame or on the DPF/SCR mounting rail.

Common Symptoms

  • Doser low fuel pressure fault
  • Failed parked regeneration attempts
  • Aftertreatment fuel pressure low or zero
  • Check engine light (CEL) illuminated
  • Active regeneration inhibited
  • Reduced DEF dosing efficiency

Root Causes

  • Open circuit in wiring harness to the aftertreatment fuel pressure control valve
  • Blown fuse or failed relay supplying power to the fuel pressure control valve circuit
  • Corroded or loose connector at the aftertreatment fuel pressure control valve
  • Failed/open aftertreatment fuel pressure control valve solenoid coil
  • Broken or chafed wiring between ACM and fuel pressure control valve
  • Poor ground connection at valve or ACM ground circuit
  • Failed ACM output driver for fuel pressure control valve circuit

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Derate Behavior

Power Derate

No

Mileage / Regen Notes

An open circuit on the aftertreatment fuel pressure control valve will inhibit active DPF regeneration. The ACM cannot properly pressurize or control fuel delivery to the burner/doser system, causing regen inhibit or regen failure faults. The vehicle may enter a limited regen or no-regen condition, potentially leading to DPF over-accumulation and derate if unresolved.

System Interactions

SPN 4766 FMI 5 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 4766 FMI 5 — 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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