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Fault Code Reference

SPN 3246 FMI 3AftertreatmentMedium

DPF Outlet Temperature 2 Sensor - Voltage High

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Overview

Fault Code

SPN 3246 / FMI 3

Category

Aftertreatment

Severity

Medium

Derate Risk

Sometimes

Regen Inhibit

No

Inducement Risk

No

Component Location: DPF outlet temperature sensor 2 is mounted on the downstream end of the DPF canister in the aftertreatment assembly, typically located under the vehicle frame mid-to-rear chassis.

Common Symptoms

  • Check engine light illuminated. MIL lamp on dash. Possible yellow engine warning lamp. Scan tool shows DPF outlet temp 2 reading pegged high or at maximum value (often 2000°F+ or maxed out). Possible reduced engine power in some applications. Regen may not complete properly if ECM cannot trust temperature readings. Exhaust temperature gauge (if equipped) may show erratic or maxed reading.

Root Causes

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Derate Behavior

Power Derate

Sometimes

Mileage / Regen Notes

This fault typically inhibits active DPF regeneration. The ACM relies on accurate DPF outlet temperature readings to control regen fuel dosing and verify regen completion. With a voltage high fault, the system cannot trust the temperature reading and will likely prevent active regen from initiating or completing. Soot loading may increase over time. Parked/stationary regen may also be blocked depending on OEM strategy. Clear fault and verify sensor operation before attempting forced regen.

System Interactions

SPN 3246 FMI 3 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
TSB Reference: No confirmed universal TSBs — verify in OEM service portal. Check for manufacturer-specific bulletins related to DPF temperature sensor harness chafing or connector corrosion. Cummins, Detroit, and Paccar have released harness reroute bulletins in the past for exhaust temp sensor wiring wear — search by VIN in OEM system.

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 3246 FMI 3 — 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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