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Fault Code Reference

SPN 2659 FMI 4EGRMedium

EGR Target Error - Voltage Low

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Overview

Fault Code

SPN 2659 / FMI 4

Category

EGR

Severity

Medium

Derate Risk

Sometimes

Regen Inhibit

No

Inducement Risk

No

Component Location: EGR mass flow calculated from MAP, MAT, and EGR valve position on ISX15; dedicated EGR flow sensor on DD15

Common Symptoms

  • Check engine light illuminated. MIL lamp on. EGR valve not responding or stuck closed. EGR flow not matching commanded target values. Possible increase in NOx emissions. Engine may run rougher at idle. Reduced fuel economy in some cases. Scan tool shows EGR position sensor voltage below normal operating range. Possible black smoke under load if EGR is stuck closed.

Root Causes

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Derate Behavior

Power Derate

Sometimes

Mileage / Regen Notes

This fault typically does not directly inhibit active DPF regeneration. However, if EGR is stuck or not functioning properly due to the circuit fault, exhaust temperatures and airflow may be affected, which can indirectly impact regen efficiency. Monitor for secondary faults related to aftertreatment temperature or soot loading that may develop if the EGR issue persists.

System Interactions

SPN 2659 FMI 4 interacts with the following systems and may trigger cascading faults if not resolved promptly.

TSB Reference: No confirmed TSBs — verify in OEM service portal. Check for manufacturer-specific bulletins related to EGR valve connector corrosion or harness chafing, especially on Cummins ISX/ISB, Detroit DD13/DD15, and Paccar MX engines where EGR harness routing near hot components is a known concern.

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.

Deep-dive diagnostic page: SPN 2659 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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