SPN 4360 FMI 4AftertreatmentMedium
SCR Intake Gas Temperature Sensor - Voltage Low
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Connector Pinout — in guided session
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Overview
Fault Code
SPN 4360 / FMI 4
Category
Aftertreatment
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: SCR inlet temperature sensor is mounted on the exhaust piping directly upstream of the SCR catalyst brick, typically on the mid-to-rear underside of the vehicle chassis near the aftertreatment assembly.
Common Symptoms
- Check engine light illuminated. MIL lamp on. SCR efficiency codes may accompany this fault. Possible DEF dosing issues due to incorrect temperature reading. Scan tool shows SCR intake temperature reading stuck at minimum value or -40°F/-40°C. Possible white smoke from tailpipe if DEF injection is affected. Reduced fuel economy if SCR system is not operating optimally.
Root Causes
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
This fault typically does NOT inhibit active DPF regeneration directly. However, the SCR inlet temperature is used by the ACM to calculate DEF dosing rates during regen. With a low voltage fault, the system may default to a substitute value or disable DEF injection to prevent overdosing. If DEF dosing is disabled, SCR efficiency will drop and could set additional NOx-related faults. Active regen can still occur but SCR catalyst performance during regen may be compromised.
System Interactions
SPN 4360 FMI 4 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 ISX15/ISB6.7 and Detroit DD13/DD15 platforms have had service bulletins addressing aftertreatment harness chafing and connector corrosion in the SCR area. Check for OEM-specific TSBs related to aftertreatment wiring harness rerouting or updated connector seals.
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 4360 FMI 4 — 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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