SPN 1185 FMI 3Electrical
Transmission Oil Pressure - Voltage Above Normal or Shorted High
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1185 / FMI 3
Category
Electrical
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Transmission oil pressure sensor is typically mounted on the transmission case near the valve body or main control solenoid assembly.
Common Symptoms
- Transmission fault lamp illuminated
- Erratic transmission shifting or limp mode
- Transmission may default to failsafe gear
- Loss of power or reduced vehicle performance
- Gear position display may be inaccurate
Root Causes
- Faulty transmission oil pressure sensor Damaged or shorted wiring harness to pressure sensor Corroded or damaged sensor connector ECM or TCM internal fault Sensor supply voltage short to battery or ignition circuit
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Derate Behavior
Power Derate
No
System Interactions
SPN 1185 FMI 3 interacts with the following systems and may trigger cascading faults if not resolved promptly.
ECM communication — J1939 network faults can affect all connected modules
Engine protection — ECM may trigger derate to prevent damage
Aftertreatment — engine protection derates can affect regen strategy
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 1185 FMI 3 — 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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