SPN 411 FMI 2Medium
EGR Differential Pressure - Data Erratic
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Overview
Fault Code
SPN 411 / FMI 2
Severity
Medium
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR differential pressure sensor is typically mounted on or near the EGR cooler or EGR valve assembly on the engine, with two small pressure hoses connecting to the inlet and outlet.
Common Symptoms
- EGR differential pressure signal erratic or unstable
- MIL or CEL illuminated
- Possible rough idle or unstable engine operation
- Reduced EGR flow control accuracy
- DPF regeneration frequency may increase
- Possible black smoke from exhaust
- Engine may enter derate or limp mode
Root Causes
- Plugged or damaged EGR differential pressure sensor ports or tubes
- Moisture or soot contamination in sensor pressure lines
- Faulty or degraded EGR differential pressure sensor
- Loose or corroded electrical connector at EGR differential pressure sensor
- Chafed, shorted, or open wiring harness to sensor
- EGR valve stuck open or partially stuck causing erratic flow
- Cracked or disconnected pressure hose/tube between sensor and EGR cooler
- ECM software issue or calibration mismatch
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Derate Behavior
Mileage / Regen Notes
Erratic EGR differential pressure data can cause inaccurate EGR flow calculations, potentially increasing particulate loading on the DPF and increasing regeneration frequency or inhibiting regen if the ECM detects unreliable sensor data.
System Interactions
SPN 411 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: EGR delta P TSBs
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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 411 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.
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.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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