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Fault Code Reference

SPN 4076 FMI 1Aftertreatment

Aftertreatment 1 Diesel Particulate Filter Differential Pressure - Data Valid But Below Normal

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Overview

Fault Code

SPN 4076 / FMI 1

Category

Aftertreatment

Derate Risk

No

Regen Inhibit

No

Inducement Risk

No

Component Location: DPF differential pressure sensor is mounted on or near the DPF canister on the exhaust aftertreatment system, typically on the driver-side frame rail or firewall area.

Common Symptoms

  • DPF differential pressure sensor reading lower than expected
  • Frequent or continuous regeneration cycles
  • Check engine light illuminated
  • Possible white smoke during regen attempts
  • Low soot load readings despite operating conditions
  • Regeneration inhibited due to implausible sensor data

Root Causes

  • Plugged or clogged low-pressure side DPF differential pressure sensor port or tubing/hose
  • DPF differential pressure sensor failed low or out of calibration
  • DPF differential pressure sensor supply or signal wire short to ground
  • Cracked, kinked, disconnected, or collapsed differential pressure sensor hose/tube
  • DPF excessively loaded with ash causing abnormally low delta-P reading due to sensor bypass
  • Moisture or soot contamination inside differential pressure sensor lines
  • DPF substrate cracked or missing, causing abnormally low differential pressure across filter
  • ACM/ECM software or calibration issue misinterpreting sensor signal

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Derate Behavior

Power Derate

No

Mileage / Regen Notes

SPN 4076 FMI 1 typically inhibits or prevents active DPF regeneration because the ACM cannot confirm a valid soot load via differential pressure; the system may also trigger a forced or inhibited regen depending on OEM strategy. Continuous low delta-P may cause the ACM to incorrectly report DPF soot level, leading to missed or skipped regen events.

System Interactions

SPN 4076 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 4076 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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