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Fault Code Reference

SPN 3510 FMI 19Medium

DEF Pressure Sensor - Data Erratic

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Overview

Fault Code

SPN 3510 / FMI 19

Severity

Medium

Regen Inhibit

No

Inducement Risk

No

Component Location: DEF pressure sensor is located on the DEF dosing unit or supply module, typically mounted near the DEF pump assembly on the frame rail or under the vehicle cab.

Common Symptoms

  • Erratic or fluctuating DEF pressure readings on scan tool datastream. DEF pressure values jumping or spiking unexpectedly without corresponding system changes. Intermittent DEF system fault lamps. Possible inconsistent DEF dosing leading to higher NOx readings. SCR efficiency codes may follow if dosing is affected. Driver may notice amber warning lamp illumination that comes and goes.

Root Causes

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Derate Behavior

Mileage / Regen Notes

FMI 19 (erratic data) on DEF pressure sensor typically does not directly inhibit active DPF regeneration since regen is primarily controlled by soot load and exhaust temps. However, if erratic pressure data causes the ACM to shut down DEF dosing as a protective measure, SCR inlet temps may be affected during regen cycles. Extended DEF system faults can indirectly impact aftertreatment performance. Monitor for secondary SCR efficiency codes which could eventually affect regen strategy.

System Interactions

SPN 3510 FMI 19 interacts with the following systems and may trigger cascading faults if not resolved promptly.

TSB Reference: No confirmed universal TSBs — verify in OEM service portal for specific chassis and engine combination. Cummins ISX and ISB platforms have had service letters regarding DEF tank header and wiring harness chafing. Detroit DD13/DD15 have had bulletins on DEF sender unit connector corrosion. Paccar MX engines check for updates on DEF pump module harness routing. Always check current OEM service information for latest applicable 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.

Deep-dive diagnostic page: SPN 3510 FMI 19 — 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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