SPN 3363 FMI 5AftertreatmentInducement Risk
Aftertreatment 1 DEF Doser 1 Absolute Pressure - Current Below Normal or Open Circuit
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
DieselVision™ Upload photos — DieselVision™ reads diagrams, connectors, and screens with precision.
Overview
Fault Code
SPN 3363 / FMI 5
Category
Aftertreatment
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: DEF doser pressure sensor is mounted on or near the DEF doser/injector assembly on the DPF/SCR aftertreatment system, typically located on the exhaust mid-pipe or SCR inlet.
Common Symptoms
- DEF system fault warning lamp illuminated
- Engine derate or power limitation
- DEF dosing system inactive or disabled
- Reduced engine performance under load
- Inducement warning or countdown timer active
Root Causes
- Open circuit in DEF doser pressure sensor supply or signal wiring harness Corroded, pushed-back, or damaged connector terminals at DEF doser pressure sensor Failed DEF doser pressure sensor (internal open circuit) Broken or chafed wiring between ACM and DEF doser pressure sensor Poor ground connection at sensor or ACM ground circuit ACM connector pin corrosion or terminal damage causing loss of sensor excitation DEF line blockage or frozen DEF causing sensor mechanical failure Failed ACM output driver for sensor supply circuit
Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.
AI walks you through every test — one step at a time. Plans start at $12.95/mo.
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 3363 FMI 5 will typically inhibit active DPF regeneration because DEF doser absolute pressure feedback is required for proper aftertreatment dosing and regen sequencing. The ACM may disable DEF injection, preventing SCR and regen operation. Continued operation may result in DPF loading, derates, and SCR NOx conversion loss. Parked and active regens will be blocked until the fault is resolved and the system is returned to normal operation.
System Interactions
SPN 3363 FMI 5 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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3363 FMI 5 — 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.
Get weekly diesel diagnostic tips
Real-world fault code walkthroughs, wiring tips, and shop-tested fixes — free.
No spam. Unsubscribe anytime.
Get AI-Guided Diagnosis for SPN 3363 FMI 5
The diagnostic engine walks you through every physical test — step by step, on your phone, at the truck. No guessing. No wasted parts.