SPN 3216 FMI 2AftertreatmentHighRegen Inhibit
Aftertreatment 1 Diesel Oxidation Catalyst Outlet Temperature - Data Erratic, Intermittent or Incorrect
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Overview
Fault Code
SPN 3216 / FMI 2
Category
Aftertreatment
Fault Type
sensor
FMI Category
erratic
Severity
High
Derate Risk
Yes
Regen Inhibit
Yes — active regen blocked
Inducement Risk
No
Component Location: DOC outlet temperature sensor threaded into the exhaust pipe between the DOC (Diesel Oxidation Catalyst) and the DPF filter. Part of the aftertreatment assembly - typically mounted under the cab or on the frame rail.
Common Symptoms
- DOC outlet temperature reading erratic or jumping in live data
- Active regeneration inhibited - ECM cannot confirm safe regen temperature
- DPF soot load increasing due to regen inhibit
- Intermittent temperature faults - fault sets and clears with vibration or temperature change
- Possible companion faults: SPN 3031 (DPF inlet temp), SPN 3242 (DPF outlet temp)
Root Causes
- DOC outlet temperature sensor connector - loose, corroded, or intermittent connection
- DOC outlet temperature sensor wiring harness - chafed or broken wire causing intermittent signal
- DOC outlet temperature sensor failure - internal intermittent fault
- Exhaust vibration causing intermittent sensor connector contact
- Moisture intrusion in sensor connector - causes erratic signal
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Derate Behavior
Power Derate
Yes
Active Regen Inhibited
This fault prevents the DPF from completing an active regeneration cycle. DPF soot load will increase until the fault is resolved.
Mileage / Regen Notes
Connector corrosion and wiring chafing increase with mileage and road exposure. Sensor failure increases with heat cycling.
System Interactions
SPN 3216 FMI 2 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: Cummins TSB 4021834 - Aftertreatment Temperature Sensor Diagnosis; Detroit TSB 18-005 - DOC/DPF Temperature Sensor Erratic Signal Diagnosis
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.
OEM Notes
Cummins
X15: DOC outlet temp sensor connector is exposed to road spray - moisture intrusion is common. Inspect connector boot seal before replacing sensor.
Detroit
DD15: Exhaust vibration causes connector wear on DD15 - check connector locking tab is fully engaged.
PACCAR
MX-13: Wiring harness routing near turbo outlet is a common chafe point. Inspect harness routing carefully.
Volvo
MP8: DOC outlet sensor failure is common at 400k+ miles on MP8. Replace sensor if resistance is unstable.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3216 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.
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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