SPN 524 FMI 4Electrical
Accelerator Pedal Position 1 - Voltage Below Normal or Shorted Low
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 524 / FMI 4
Category
Electrical
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: Accelerator pedal position sensor is mounted at the top of the accelerator pedal assembly in the driver compartment.
Common Symptoms
- Check engine light/MIL illuminated
- Engine operates at low idle only
- No throttle response from accelerator pedal
- Engine may run but not respond to pedal input
- Limp mode operation
- Cruise control disabled
Root Causes
- Damaged or chafed wiring harness between accelerator pedal sensor and ECM Faulty accelerator pedal position sensor Corroded or loose connector at accelerator pedal sensor Short to ground in accelerator pedal position sensor circuit Water intrusion into accelerator pedal sensor connector
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Derate Behavior
Power Derate
Yes
System Interactions
SPN 524 FMI 4 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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 524 FMI 4 — 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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