SPN 2202 FMI 0Emissions
NOx Sensor Circuit Low Bank 1
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Connector Pinout — in guided session
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Overview
Fault Code
SPN 2202 / FMI 0
Category
Emissions
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Downstream NOx sensor is mounted in the exhaust aftertreatment system, typically on the outlet cone of the SCR catalyst, behind the DPF/SCR assembly.
Common Symptoms
- Check engine light or MIL illuminated
- DEF/SCR system warning lamp active
- NOx sensor voltage reading below normal range on diagnostic scan
- Possible derate or engine power reduction in emissions-critical modes
- Failed emissions test or OBD readiness monitor not complete
- Excessive NOx output detected during active regen or SCR operation
Root Causes
- Failed or contaminated downstream NOx sensor (sensor aging, thermal damage, or water intrusion)
- NOx sensor heater circuit failure causing sensor not reaching operating temperature
- Wiring harness damage or chafing between NOx sensor and ECM/ACM connector
- Poor or corroded connector at NOx sensor harness plug causing high resistance
- SCR catalyst degradation causing abnormally low NOx readings triggering rationality fault
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Derate Behavior
Power Derate
No
Mileage / Regen Notes
SPN 2202 FMI 0 will typically inhibit or disable active DPF regeneration and may place the aftertreatment system in a derate or limp mode; SCR dosing efficiency cannot be confirmed without a valid NOx signal, potentially triggering additional SCR-related faults.
System Interactions
SPN 2202 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.
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 2202 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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