SPN 27 FMI 4EGRHigh
EGR Valve Position — Voltage Below Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 27 / FMI 4
Category
EGR
Fault Type
sensor
FMI Category
voltage low
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR valve position sensor — on EGR valve assembly
Common Symptoms
- EGR valve position sensor reading low or zero
- Engine derate
- EGR system not controlling
Root Causes
- EGR position sensor open circuit
- 5V reference open
- Ground circuit open
- Sensor failed open
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
Open circuit faults common at 200k–350k miles.
System Interactions
SPN 27 FMI 4 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: Cummins TSB 4021301 — EGR Position Sensor Open Circuit
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.
OEM Notes
Cummins
X15: Check harness routing near EGR cooler for heat damage.
Detroit
DD15: Check connector for moisture intrusion.
PACCAR
MX-13: Inspect connector boot for cracks.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 27 FMI 4 — 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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