SPN 4340 FMI 2EGR
EGR Temperature Sensor - Erratic/Intermittent
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Overview
Fault Code
SPN 4340 / FMI 2
Category
EGR
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR temperature sensor is mounted on the EGR cooler outlet or EGR mixing pipe, typically on the engine's exhaust side near the intake manifold.
Common Symptoms
- Intermittent or fluctuating EGR temperature readings
- Check engine light/MIL illuminated
- Reduced engine power or performance
- Increased emissions
- Poor fuel economy
- Rough idle or hesitation
Root Causes
- Damaged or corroded EGR temperature sensor connector/harness
- Faulty EGR temperature sensor with intermittent internal failure
- Chafed or shorted wiring harness near exhaust components causing signal dropouts
- Poor sensor ground connection at ECM or chassis ground point
- Heat-damaged wiring insulation near EGR cooler or exhaust manifold
- Loose or backed-out terminal pins at sensor connector
- ECM connector corrosion or intermittent internal ECM fault
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Derate Behavior
Power Derate
No
Mileage / Regen Notes
An erratic EGR temperature sensor signal may inhibit or abort active DPF regeneration cycles, as the ECM relies on accurate EGR temperature data to confirm safe regen conditions. Regen inhibit or derate conditions may be triggered depending on OEM calibration thresholds.
System Interactions
SPN 4340 FMI 2 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.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4340 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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