SPN 1807 FMI 31AftertreatmentInducement Risk
DEF Tank Heater - Condition Exists
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Overview
Fault Code
SPN 1807 / 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 directly on the DEF tank, typically located on the frame rail or crossmember beneath the cab or behind the fuel tank.
Common Symptoms
- DEF tank heater active indicator on
- DEF heater running continuously in cold ambient conditions
- DEF heater cycling frequently
- No driveability symptoms typically present
- Fault logged as informational condition exists code
Root Causes
- DEF tank heater circuit open or short to ground Failed DEF tank heater element (burned out or open circuit) Corroded or damaged connector at DEF tank heater plug Blown fuse or failed relay in DEF heater supply circuit Faulty ACM (Aftertreatment Control Module) output driver Chafed or broken wiring harness between ACM and DEF tank heater DEF tank assembly failure requiring full tank replacement
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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 1807 FMI 31 may inhibit or delay DPF regeneration in cold ambient conditions if the DEF system cannot be confirmed operational; the ACM may prevent dosing and regen until DEF fluid temperature is verified within acceptable range.
System Interactions
SPN 1807 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.
Related Faults in This Category
OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1807 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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