SPN 412 FMI 2Medium
EGR Temperature - Data Erratic
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Overview
Fault Code
SPN 412 / FMI 2
Severity
Medium
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR temperature sensor is mounted on the EGR cooler outlet or EGR mixer/valve assembly, typically on the driver side of the engine near the intake manifold.
Common Symptoms
- Erratic or fluctuating EGR temperature sensor readings
- Intermittent MIL or CEL illumination
- EGR system entering limp mode or defaulting to fixed value
- Rough idle or poor throttle response
- Increased NOx emissions or failed emissions test
- DPF regeneration events more frequent or inhibited
- Engine derate in some operating conditions
Root Causes
- Faulty or degraded EGR temperature sensor (thermistor failure causing erratic signal) Loose, corroded, or damaged connector at EGR temperature sensor Chafed or shorted wiring harness near exhaust/EGR cooler heat source EGR cooler fouling or blockage causing abnormal temperature swings Poor sensor ground or reference voltage instability Intermittent open circuit in signal wire due to vibration ECM/ECU software fault or calibration mismatch Carbon buildup on sensor tip causing delayed or erratic thermal response
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Derate Behavior
Mileage / Regen Notes
SPN 412 FMI 2 may inhibit or disrupt active DPF regeneration if the ECM cannot reliably determine EGR system thermal state; some platforms will default to a fixed EGR temperature value and allow limited regen while others will suspend regen until the fault is resolved.
System Interactions
SPN 412 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: EGR temp TSBs
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
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 412 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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