SPN 4332 FMI 3AftertreatmentInducement Risk
SCR Catalyst Outlet Temperature - Voltage Above Normal or Shorted High
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Overview
Fault Code
SPN 4332 / FMI 3
Category
Aftertreatment
Derate Risk
No
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: SCR outlet temperature sensor is mounted on the outlet cone or tailpipe section of the SCR catalyst canister, typically on the downstream exhaust piping behind the DEF injection point.
Common Symptoms
- Check engine light or malfunction indicator lamp illuminated
- Engine derate or power loss
- Exhaust temperature gauge reading abnormally high or erratic
- DEF dosing system may operate abnormally
- Possible exhaust aftertreatment system warning messages
Root Causes
- Open or shorted signal wire in SCR outlet temperature sensor harness (wire shorted to voltage source) Damaged or corroded connector at SCR outlet temperature sensor Failed SCR outlet temperature sensor (internal short to high voltage) Chafed wiring contacting exhaust component or chassis creating short to power ACM or ECM sensor supply voltage fault feeding back into signal circuit Water intrusion into connector causing elevated signal voltage
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Derate Behavior
Power Derate
No
SCR Inducement Risk
If left unresolved, this fault may trigger SCR inducement — a progressive derate enforced by the ECM to ensure emissions compliance.
Mileage / Regen Notes
An active SPN 4332 FMI 3 fault on the SCR outlet temperature sensor will typically inhibit or abort active DPF regeneration cycles, as the ACM cannot confirm safe SCR outlet temperatures. Forced or parked regen may be blocked. The aftertreatment system may enter a derate or limited operation strategy depending on OEM programming.
System Interactions
SPN 4332 FMI 3 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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4332 FMI 3 — 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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