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Fault Code Reference

SPN 3245 FMI 2AftertreatmentInducement Risk

DEF Tank Level - Data Erratic

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Overview

Fault Code

SPN 3245 / FMI 2

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: DEF level sensor is mounted on or inside the DEF tank, typically on the top or side of the tank located under the cab or along the frame rail on the passenger side.

Common Symptoms

  • DEF level gauge reading erratic or jumping
  • Intermittent DEF system warnings on dash
  • DEF low level warning despite full tank
  • Engine derate countdown initiated
  • Check engine light illuminated

Root Causes

  • Faulty or contaminated DEF level sensor (float/ultrasonic type) DEF tank contamination (diesel, water, or other fluid in tank) causing erratic float behavior Corroded or damaged DEF level sensor connector/harness Open or intermittent circuit in DEF level sensor wiring harness DEF tank sensor ground circuit fault or high resistance ground Failed or cracked DEF level sensor float assembly ACM/DCU software issue or calibration mismatch requiring reflash DEF tank itself cracked or deformed affecting sensor mounting

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Derate Behavior

Power Derate

Yes

SCR Inducement Risk

If left unresolved, this fault may trigger SCR inducement — a progressive derate enforced by the ECM to ensure emissions compliance.

Mileage / Regen Notes

SPN 3245 FMI 2 (DEF Tank Level Data Erratic) can inhibit active DPF regeneration and may trigger SCR/DEF system derate if the ACM cannot determine a reliable DEF level. Depending on OEM strategy, the system may default to a worst-case low-DEF assumption, triggering inducement (torque derate or speed limiting) after fault timers expire. Regen inhibit thresholds and inducement timelines vary by OEM and fault persistence duration.

System Interactions

SPN 3245 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.

DPF differential pressure monitoring — soot load calculations affected
SCR NOx conversion efficiency — DEF dosing strategy may be altered
Active regen inhibit logic — regen may be blocked or delayed
Engine protection derate — ECM may reduce power to protect components

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.

Replacing the DPF without verifying the regen system is functional — a failed regen injector will reload the new DPF.

Ignoring DEF quality — contaminated DEF causes SCR efficiency faults that look like hardware failures.

Deep-dive diagnostic page: SPN 3245 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.

EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx 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.

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