SPN 3697 FMI 18AftertreatmentInducement Risk
Aftertreatment Fuel Pressure 2 - Data Valid But Below Normal
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Overview
Fault Code
SPN 3697 / FMI 18
Category
Aftertreatment
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: Aftertreatment fuel pressure sensor 2 is located on the aftertreatment fuel doser system plumbing, typically near the HC doser pump or doser injector on the exhaust aftertreatment assembly.
Common Symptoms
- DEF doser inoperative or reduced performance
- Aftertreatment fuel injector poor atomization
- Failed or incomplete regenerations
- SCR efficiency codes
- Check engine light/MIL illuminated
- Low aftertreatment fuel delivery
Root Causes
- Clogged or restricted aftertreatment fuel supply line to doser injector Failing or weak aftertreatment fuel pump (HC doser pump) with insufficient output pressure Partially blocked aftertreatment fuel filter or strainer Leaking or stuck-open doser injector causing pressure bleed-down Air ingestion in aftertreatment fuel supply system Faulty aftertreatment fuel pressure sensor 2 giving low reading Low fuel tank level causing fuel starvation to doser system Kinked, damaged, or collapsed aftertreatment fuel supply line
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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
FMI 18 on SPN 3697 will inhibit or abort active DPF regeneration cycles because the ACM requires adequate aftertreatment fuel pressure to operate the HC doser injector for thermal management. Repeated or sustained low-pressure faults may trigger a regen inhibit lamp and place the system in a derate or regen lockout condition until the fault is resolved.
System Interactions
SPN 3697 FMI 18 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
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3697 FMI 18 — 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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