SPN 3242 FMI 5AftertreatmentMedium
DPF Outlet Temperature Sensor - Current Below Normal
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 3242 / FMI 5
Category
Aftertreatment
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: DPF outlet temperature sensor is mounted on the downstream (outlet) end of the diesel particulate filter, typically along the exhaust pipe or filter canister exit.
Common Symptoms
- DPF outlet temp not reading correctly
Root Causes
- Open circuit in wiring harness between DPF outlet temperature sensor and ECM/ACM Corroded or damaged connector at DPF outlet temperature sensor Faulty or failed DPF outlet temperature sensor (thermistor open circuit) Broken or damaged sensor signal or ground wire causing loss of current Poor pin contact or backed-out terminal in sensor connector or ECM connector Chafed or shorted wiring harness near exhaust/heat source causing open circuit Failed ECM/ACM with open internal circuit on sensor input channel
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
Outlet temp sensor open circuit — check wiring before replacing.
System Interactions
SPN 3242 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 3242 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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