SPN 3216 FMI 5AftertreatmentMedium
Intake NOx Sensor - Current Below Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 3216 / FMI 5
Category
Aftertreatment
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: The intake NOx sensor is located in the intake manifold or intake air ducting upstream of the combustion chamber.
Common Symptoms
- MIL lamp illuminated. Erratic, stuck, or no intake NOx reading on scan tool. NOx sensor reading shows 0 ppm or drops out intermittently. Possible DEF dosing issues due to faulty NOx feedback. Ammonia slip or over-dosing of DEF if system compensates incorrectly. May see related outlet NOx sensor codes if system loses reference for SCR efficiency calculations.
Root Causes
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
This fault typically does not inhibit active regeneration directly. However, the intake NOx sensor provides baseline data for SCR efficiency monitoring. With erratic or missing intake NOx data, the system may have difficulty calculating DEF dosing and SCR conversion rates. Prolonged operation may cause secondary codes related to SCR efficiency (SPN 4364/4365) which CAN inhibit regen. Address promptly to avoid cascading aftertreatment issues.
System Interactions
SPN 3216 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
TSB Reference: No confirmed universal TSBs — verify in OEM service portal. Cummins ISX/X15: Check for bulletins on NOx sensor harness chafing near turbo and DPF. Detroit DD13/DD15: Check for service letters on aftertreatment harness routing. Paccar MX: Review known issues with connector sealing at NOx sensors.
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 3216 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.
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