SPN 2633 FMI 0NOxInducement Risk
NOx Sensor Circuit High Bank 1
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 2633 / FMI 0
Category
NOx
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: Bank 1 NOx sensor is typically located in the exhaust stream downstream of the SCR catalyst assembly.
Common Symptoms
- Check engine light illuminated
- Engine derate or power loss
- SCR system efficiency fault codes present
- Increased DEF consumption reported
- NOx sensor data reading above normal range or implausible
Root Causes
- Faulty NOx sensor on Bank 1 Damaged or corroded wiring harness to NOx sensor Water intrusion or contamination in NOx sensor connector Exhaust leaks near NOx sensor causing erroneous readings ECM software calibration issue
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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.
System Interactions
SPN 2633 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 2633 FMI 0 — 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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