SPN 1478 FMI 0EGR
EGR Cooler Bypass Control Circuit Low
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1478 / FMI 0
Category
EGR
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The EGR cooler bypass valve actuator is mounted on or near the EGR cooler assembly in the intake system.
Common Symptoms
- Check engine light illuminated
- EGR system fault codes present
- Possible engine derate in some conditions
- Reduced fuel economy
- Increased NOx emissions
Root Causes
- EGR cooler bypass valve actuator short to ground in control circuit Chafed or damaged wiring harness causing low voltage condition on EGR bypass control circuit Corroded or moisture-contaminated ECM connector pins on EGR bypass control circuit Failed EGR cooler bypass valve solenoid with internal short to ground Corroded or loose ground connection at EGR bypass actuator or ECM ECM internal driver failure causing low circuit output
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Derate Behavior
Power Derate
No
System Interactions
SPN 1478 FMI 0 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 1478 FMI 0 — 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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