SPN 1347 FMI 18EGR
EGR Differential Pressure - Data Valid But Below Normal
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Overview
Fault Code
SPN 1347 / FMI 18
Category
EGR
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR differential pressure sensor is typically mounted on the EGR system near the EGR valve or cooler outlet, with two pressure port hoses connecting upstream and downstream of the EGR flow restriction.
Common Symptoms
- Check engine light illuminated
- Engine derate or reduced power
- Poor fuel economy
- Increased exhaust smoke
- EGR system not functioning properly
- Possible rough idle or hesitation
Root Causes
- Clogged or restricted EGR differential pressure sensor ports or tubing (carbon/soot buildup) Failed or degraded EGR differential pressure sensor (low output signal) EGR valve stuck closed or not opening sufficiently causing low differential pressure Carbon buildup on EGR cooler passages reducing flow and pressure differential Plugged EGR delta pressure reference hoses or fittings Cracked, kinked, or disconnected pressure sensing lines/tubes EGR valve actuator failure or weak operation EGR differential pressure sensor ground degradation causing signal offset Intake throttle valve not closing properly reducing EGR driving pressure differential ECM calibration or software issue causing incorrect threshold interpretation
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Derate Behavior
Power Derate
No
Mileage / Regen Notes
SPN 1347 FMI 18 (EGR differential pressure below normal) may inhibit or delay active DPF regeneration on many platforms, as the ECM requires confirmed EGR flow validation before enabling regen conditions. Extended low EGR flow can also accelerate DPF loading, increasing regen frequency.
System Interactions
SPN 1347 FMI 18 interacts with the following systems and may trigger cascading faults if not resolved promptly.
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
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1347 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.
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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