SPN 5560 FMI 31AftertreatmentInducement Risk
Aftertreatment DEF Tank Heater - Condition Exists
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Overview
Fault Code
SPN 5560 / FMI 31
Category
Aftertreatment
Derate Risk
No
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: DEF tank heater is integrated into or mounted on the DEF tank assembly, typically located on the vehicle frame rail or under-cab area near the DEF tank.
Common Symptoms
- DEF tank heater not operating in cold ambient conditions
- DEF quality gauge shows poor quality or frozen DEF
- Slow or no DEF consumption during cold weather operation
- DEF system inducement warning active
- DEF tank temperature remains low despite heater command
Root Causes
- DEF tank heater circuit open or short to ground Blown fuse in DEF heater supply circuit Faulty DEF tank heater element (internal open circuit) Poor or corroded connector at DEF tank heater harness Failed Aftertreatment Control Module (ACM) heater driver output Damaged wiring harness between ACM and DEF tank heater DEF tank heater relay failure Low or no supply voltage to DEF heater circuit
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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
SPN 5560 FMI 31 indicates a DEF tank heater condition exists; in cold ambient temperatures this may inhibit DEF dosing capability, which can prevent or inhibit active DPF/SCR regeneration and lead to SCR system derating if DEF remains frozen.
System Interactions
SPN 5560 FMI 31 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 5560 FMI 31 — 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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