SPN 3702 FMI 31AftertreatmentInducement Risk
DPF Regeneration Conditions Not Met - Condition Exists
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 3702 / FMI 31
Category
Aftertreatment
Derate Risk
No
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: DPF is mounted in the exhaust system downstream of the turbocharger and diesel oxidation catalyst.
Common Symptoms
- DPF regeneration does not initiate when expected
- Continuous DPF regeneration request or lamp illuminated
- Elevated exhaust backpressure readings
- Engine derate due to excessive DPF soot loading
- Frequent parked regeneration requests
Root Causes
- Insufficient exhaust temperature to initiate or sustain DPF regeneration (low load/idle operation) Inhibited regeneration due to active fault codes blocking regen (e.g., DOC, DPF, or NOx sensor faults) Low fuel level inhibiting parked regen initiation Faulty or biased exhaust temperature sensors preventing accurate thermal assessment Excessive soot load beyond regeneration recovery threshold Engine operating in conditions not suitable for regen (frequent short trips, cold ambient temperatures) DEF quality or dosing issues causing SCR-related inhibits that block regen Aftertreatment fuel injector (AFI) fault or clogging preventing active regen DPF differential pressure sensor fault providing incorrect soot load estimation ACM software or calibration issue misinterpreting regen enable conditions
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.
Derate Behavior
Power Derate
No
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 3702 FMI 31 directly indicates that DPF regeneration conditions are not currently met. Active regen is inhibited until all enable conditions are satisfied. Parked and active regen will not initiate. Extended inhibit increases soot load risk leading to DPF damage or derate.
System Interactions
SPN 3702 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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3702 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 3702 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.