SPN 3242 FMI 2Medium
DPF Outlet Temperature - Data Erratic
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Connector Pinout — in guided session
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Overview
Fault Code
SPN 3242 / FMI 2
Severity
Medium
Regen Inhibit
No
Inducement Risk
No
Component Location: DPF outlet temperature sensor is mounted on the downstream face or outlet pipe of the diesel particulate filter, typically mid-chassis on the aftertreatment assembly.
Common Symptoms
- DPF outlet temperature reading fluctuates erratically or is unstable
- Intermittent or missing temperature data in diagnostic software
- Active or pending fault code for SPN 3242 FMI 2
- Inhibited or interrupted DPF regeneration cycle
- SCR system may be affected if downstream temp data is shared
- MIL or amber warning lamp illuminated
Root Causes
- Faulty or degraded DPF outlet temperature sensor (thermocouple or thermistor)
- Loose, corroded, or damaged connector at the DPF outlet temperature sensor
- Chafed, shorted, or open wiring harness between sensor and ACM/ECM
- Sensor exposed to excessive moisture or road debris causing internal failure
- Poor ground connection at the aftertreatment module or sensor ground circuit
- EMI/RFI interference causing erratic signal on the sensor circuit
- Failed or intermittent aftertreatment control module (ACM)
- Exhaust leak near sensor affecting reading accuracy
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Derate Behavior
Mileage / Regen Notes
SPN 3242 FMI 2 typically inhibits active DPF regeneration because the aftertreatment control module requires valid outlet temperature data to safely monitor and control the regen process. Automatic and manual regens may be blocked until the fault is resolved.
System Interactions
SPN 3242 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: DPF temp TSB
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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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3242 FMI 2 — 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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