AI Diesel Tech

Fault Code Reference

SPN 2795 FMI 31AftertreatmentInducement Risk

Diesel Particulate Filter System High Soot Level - Condition Exists

Run Full DiagnosisView Related FaultsSee OEM System Guide

Scan Tool — in guided session

DVOM Testing — in guided session

Connector Pinout — in guided session

DieselVision™ Upload photos — DieselVision™ reads diagrams, connectors, and screens with precision.

Overview

Fault Code

SPN 2795 / FMI 31

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: DPF assembly is mounted in the exhaust stream downstream of the DOC, typically on the chassis rail or under the cab/frame behind the engine compartment.

Common Symptoms

  • DPF regeneration frequency increased
  • Check engine light or DPF lamp illuminated
  • Vehicle power reduction or derate condition
  • Excessive exhaust backpressure
  • Poor fuel economy
  • Black smoke from exhaust during acceleration
  • Engine may run rough or hesitate under load

Root Causes

  • Excessive soot accumulation due to failed or incomplete DPF regeneration cycles
  • Faulty or clogged DPF differential pressure sensor causing inaccurate soot load readings
  • Plugged or damaged DPF substrate restricting exhaust flow
  • Faulty exhaust back pressure sensor or delta-P sensor lines blocked with soot/water
  • Frequent short-trip or low-load duty cycles preventing passive regen
  • Faulty diesel oxidation catalyst (DOC) failing to generate sufficient heat for active regen
  • Low exhaust temperatures due to engine issues (misfires, low compression, injector problems)
  • Blocked or leaking delta-P sensor hoses/tubes causing false high soot readings
  • Faulty ACM or corrupted regen inhibit logic preventing regen initiation
  • Ash loading exceeding service interval requiring DPF cleaning or replacement

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.

Start Guided DiagnosisSee How It Works

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

SPN 2795 FMI 31 indicates the DPF soot level has exceeded a critical threshold. Active and passive regeneration may be inhibited or failing to complete. The ACM will request forced regen; if soot load reaches maximum threshold, engine derate and torque limiting will be applied. Vehicle may enter a limp-home mode with reduced power until DPF soot level is reduced through a successful regeneration or physical service.

System Interactions

SPN 2795 FMI 31 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 2795 FMI 31 — 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.

Get weekly diesel diagnostic tips

Real-world fault code walkthroughs, wiring tips, and shop-tested fixes — free.

No spam. Unsubscribe anytime.

Get AI-Guided Diagnosis for SPN 2795 FMI 31

The diagnostic engine walks you through every physical test — step by step, on your phone, at the truck. No guessing. No wasted parts.

Run Full DiagnosisView Related FaultsSee OEM System Guide