SPN 3701 FMI 2AftertreatmentInducement Risk
DPF Regeneration Maximum Temperature Not Achieved - Data Erratic
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Overview
Fault Code
SPN 3701 / FMI 2
Category
Aftertreatment
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: DPF inlet and outlet temperature sensors are mounted in the exhaust system before and after the diesel particulate filter.
Common Symptoms
- DPF regeneration does not complete successfully
- Frequent regeneration requests or extended regen cycles
- Engine derate or power loss during regen attempts
- High exhaust system protection warning
- Elevated exhaust temperatures but regeneration fails to complete
- DPF lamp illuminated or amber warning light active
Root Causes
- Faulty or degraded diesel oxidation catalyst (DOC) unable to generate sufficient exotherm Clogged or damaged DPF preventing proper temperature distribution during regen Malfunctioning hydrocarbon (HC) doser/injector not delivering adequate fuel for exotherm Erratic or failed aftertreatment DPF outlet temperature sensor (Temp Sensor 3/4) Failed or failing aftertreatment DPF inlet temperature sensor providing erratic data Exhaust system air leaks upstream of DPF reducing regen efficiency Low fuel pressure to HC doser causing inconsistent hydrocarbon injection Plugged or restricted HC doser nozzle ACM software/calibration issue causing erratic temperature interpretation Intermittent wiring or connector fault at temperature sensor harness
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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
SPN 3701 FMI 2 indicates that during an active DPF regeneration event, the maximum required temperature was not achieved and sensor data was erratic. This will typically inhibit or abort active regen cycles, increment DPF soot load, and may result in a forced regen lockout or reduced engine power derate if soot load reaches critical threshold.
System Interactions
SPN 3701 FMI 2 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 3701 FMI 2 — 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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