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Fault Code Reference

SPN 3216 FMI 19Medium

Intake NOx Sensor - Data Erratic

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Overview

Fault Code

SPN 3216 / FMI 19

Severity

Medium

Regen Inhibit

No

Inducement Risk

No

Component Location: The intake NOx sensor is mounted in the intake manifold or air intake system upstream of the combustion chamber.

Common Symptoms

  • MIL lamp illuminated. Erratic or fluctuating NOx readings on scan tool that don't correlate with engine load or exhaust conditions. Intermittent fault codes setting and clearing. Possible false SCR efficiency faults (SPN 4364/4365) due to unreliable inlet NOx data. DEF dosing may be erratic or incorrect. Possible phantom high or low NOx spikes in data stream. May see related communication faults for NOx sensor CAN network.

Root Causes

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Derate Behavior

Mileage / Regen Notes

FMI 19 (data erratic) on the intake NOx sensor typically does not directly inhibit active regeneration since the inlet sensor is primarily used for SCR efficiency monitoring rather than regen control. However, if the ACM cannot get reliable NOx data, DEF dosing strategy may be affected which can lead to downstream SCR efficiency faults. If multiple NOx-related codes set, active regen may be inhibited until reliable sensor data is restored. Monitor regen status with scan tool — if regen is inhibited, address this fault promptly to prevent soot accumulation.

System Interactions

SPN 3216 FMI 19 interacts with the following systems and may trigger cascading faults if not resolved promptly.

TSB Reference: No confirmed TSBs — verify in OEM service portal. Continental and Cummins have issued service letters regarding NOx sensor connector sealing and harness routing on certain applications. Check for applicable bulletins by VIN for sensor replacement procedures and updated part numbers.

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 3216 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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