SPN 3220 FMI 16Aftertreatment
Aftertreatment 1 Diesel Particulate Filter Differential Pressure - Data Valid But Above Normal
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Overview
Fault Code
SPN 3220 / FMI 16
Category
Aftertreatment
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: DPF differential pressure sensor mounts on or near the DPF canister in the aftertreatment system, typically on the mid to rear underside of the chassis or in the exhaust tunnel.
Common Symptoms
- Engine derate or power reduction
- Check engine light illuminated
- Excessive active regeneration attempts
- Poor fuel economy
- High exhaust backpressure warning
- DPF regeneration requests more frequent than normal
Root Causes
- Plugged or heavily loaded DPF requiring forced or parked regeneration Failed or incomplete regeneration cycle (interrupted regen, short duty cycles) DPF differential pressure sensor malfunction or drift (reading high falsely) Clogged or cracked differential pressure sensor hoses/tubes (restriction causing elevated reading) DPF inlet or outlet pressure port plugged with soot or debris DOC degradation reducing upstream temperature and preventing effective regen Excessive oil consumption causing DPF ash loading beyond serviceable limit Fuel injector issues causing excess soot generation EGR system malfunction increasing soot load on DPF DEF/SCR dosing issues indirectly masking high backpressure conditions
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
SPN 3220 FMI 16 directly indicates elevated DPF differential pressure above normal operational threshold. Active regen may be triggered or may already be in progress. If soot load reaches critical levels, regen will be forced or inhibited depending on OEM logic. Parked regen may be required. Continued elevation may result in derate (torque and/or speed limitation) and engine shutdown protection on some platforms. Regen inhibit conditions such as low coolant temp, active faults, or low DEF will block recovery.
System Interactions
SPN 3220 FMI 16 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
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3220 FMI 16 — 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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