SPN 3244 FMI 2Aftertreatment
Aftertreatment Fuel Pressure 1 - Data Erratic
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Overview
Fault Code
SPN 3244 / FMI 2
Category
Aftertreatment
Derate Risk
Possible
Regen Inhibit
No
Inducement Risk
No
Component Location: Aftertreatment fuel pressure sensor is located on the fuel supply line feeding the HC dosing injector, typically mounted on or near the aftertreatment fuel pump module on the chassis.
Common Symptoms
- Aftertreatment fuel pressure fluctuating or unstable
- DPF regeneration failing to complete or aborting mid-cycle
- Dosing valve actuation irregular or inconsistent
- White smoke during regeneration attempts
- Check engine light illuminated with aftertreatment fault
- Reduced DEF dosing performance
Root Causes
- Faulty or contaminated aftertreatment fuel pressure sensor Air in the aftertreatment fuel supply line causing erratic pressure readings Plugged or restricted aftertreatment fuel filter/strainer Failing or intermittent aftertreatment dosing pump Wiring harness chafing or intermittent open/short to the sensor signal circuit Loose or corroded sensor connector causing signal dropout ACM software or calibration issue causing misinterpretation of sensor data
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Derate Behavior
Power Derate
Possible
Mileage / Regen Notes
SPN 3244 FMI 2 will inhibit active DPF regeneration. The ACM cannot confirm stable fuel pressure for the HC dosing injector, so regen is blocked to prevent injector damage or uncontrolled combustion in the aftertreatment system.
System Interactions
SPN 3244 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
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3244 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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