SPN/FMI Codes
Learn how Suspect Parameter Numbers and Failure Mode Identifiers work in heavy-duty diagnostics.
Truck Fault Code Lookup
A free, independent source-verified educational reference for heavy-duty truck fault codes, SPN/FMI terms, J1939 diagnostics, ABS codes, transmission codes, symptoms, systems, and ELD malfunction categories.
Main Lookup Areas
FMI Codes
Browse FMI 0 through FMI 31 with cautious plain-English diagnostic context.
J1939 Basics
A plain-English introduction to the vehicle network used by modern heavy-duty trucks.
J1939 Topics
Focused guides to SPN, FMI, source address, PGN, CAN bus, and data link terminology.
Cummins Fault Codes
Context for Cummins ECM faults, aftertreatment faults, and source verification needs.
Detroit Diesel Fault Codes
DD13, DD15, and DD16 fault code categories with careful source-backed framing.
Bendix ABS Fault Codes
Brake and stability code categories for Bendix ABS, ATC, and ESP systems.
WABCO ABS Fault Codes
Trailer ABS, EBS, blink codes, and SPN/FMI context for WABCO/ZF systems.
Eaton Transmission Fault Codes
Overview of AutoShift, UltraShift, and Endurant fault code formats.
ELD Malfunction Codes
FMCSA-backed explanations of ELD malfunctions and data diagnostic events.
Truck Systems
Educational system pages for aftertreatment, ABS, DPF, SCR, transmission, and data link issues.
Truck Symptoms
Symptom-based entry points for warning lights, derate, ABS lamps, DPF lights, and ELD indicators.
Manufacturer Hubs
Brand and supplier context pages for official verification paths and related systems.
SPN Topic Pages
Focused SPN number topic pages that explain what to record and why FMI context matters.
Diagnostic Education
Practical guides for recording codes, reading warning lights, and preparing technician notes.
Component Context
Component-level educational pages for sensors, modules, aftertreatment, brakes, transmission, and ELD hardware.
ELD Compliance Education
FMCSA and eCFR source-backed ELD malfunction, driver, and carrier education pages.
ELD Data Diagnostic Events
FMCSA-backed explanations of ELD data diagnostic event categories and how to handle them.
Fault Code Tools
Static browser-only decoders, note templates, and technician call checklists.
How To Read A Truck Fault Code
Many heavy-duty diagnostic messages combine a system identifier with a failure description. In J1939, the SPN points to the parameter being reported, while the FMI describes the type of abnormal condition. OEM fault numbers may add manufacturer-specific mapping that depends on engine serial number, model year, calibration, and diagnostic software version.
Always record the full code, active or inactive status, warning lamps, derate state, and related codes before drawing conclusions. A code is a starting point for diagnosis, not proof that a specific part has failed.
Learn SPN/FMI basics Browse systems Browse symptoms Diagnostic guides Manufacturer hubs
Source-Verified Fault Code Pages
Each page below is tied to an official, government, or OEM source. Records without a verifiable source are excluded from search and sitemap.
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ELD Power Malfunction
Electronic Logging Device · Power compliance monitoring
Source-backed explanation of an ELD power malfunction or power data diagnostic event under FMCSA ELD rules.
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ELD Engine Synchronization Malfunction
Electronic Logging Device · Engine ECM data connection
FMCSA-backed explanation of ELD engine synchronization data diagnostic events and malfunctions.
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ELD Timing Malfunction
Electronic Logging Device · Time synchronization
Conservative explanation of ELD timing compliance malfunctions using FMCSA and CFR sources.
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ELD Positioning Malfunction
Electronic Logging Device · Position measurement
FMCSA-backed explanation of ELD positioning compliance malfunctions and location data concerns.
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ELD Data Recording Malfunction
Electronic Logging Device · Record storage and retrieval
Source-backed explanation of ELD data recording compliance malfunctions and first checks.
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ELD Data Transfer Malfunction
Electronic Logging Device · Roadside data transfer
FMCSA-backed explanation of ELD data transfer diagnostic events and compliance malfunctions.
FAQ
What is an SPN and FMI in a truck fault code?
SPN stands for Suspect Parameter Number — it identifies which system or parameter the ECM is reporting on. FMI stands for Failure Mode Identifier — it describes the type of fault, such as signal out of range, short to ground, or erratic data. Together they form the core of a J1939 diagnostic message used in most modern heavy-duty trucks.
Does a fault code mean a specific part has failed?
Not necessarily. A fault code tells you what the control module observed, not which part has definitively failed. The same code can result from a bad sensor, wiring issue, connector corrosion, ECM calibration mismatch, or an actual component failure. Always record the full code, active or inactive status, related codes, and warning lamps before drawing conclusions.
Is this site affiliated with Cummins, Freightliner, Detroit Diesel, or any OEM?
No. This is an independent educational reference and is not affiliated with, endorsed by, or sponsored by any OEM, manufacturer, or government agency. Always verify diagnostic steps with official OEM service information and qualified technicians.