SPN 4363 FMI 5AftertreatmentMedium
SCR Outlet Temperature Sensor - Current Below Normal
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Connector Pinout — in guided session
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Overview
Fault Code
SPN 4363 / FMI 5
Category
Aftertreatment
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: SCR outlet temperature sensor mounted on the exhaust pipe downstream of the SCR catalyst brick, typically near the tailpipe end of the aftertreatment assembly.
Common Symptoms
- SCR outlet temp not reading
Root Causes
- Open circuit in the SCR outlet temperature sensor signal or supply wire
- Corroded, damaged, or disconnected wiring harness connector at the SCR outlet temperature sensor
- Broken or chafed wiring between the sensor and the aftertreatment control module
- Failed SCR outlet temperature sensor (open internal element)
- Poor or missing sensor ground connection
- Damaged aftertreatment wiring harness due to heat exposure near exhaust components
- Faulty aftertreatment control module (ACM) or engine control module (ECM) with open input circuit
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
Outlet temp sensor open circuit — check wiring before replacing.
System Interactions
SPN 4363 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
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.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4363 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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