What is this Fault code on your display? Click the button to find out
It could be DTC or SPN
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Frequently Asked Questions
Please reach us at faulty@faultcodefinder.com if you cannot find an answer to your question.
Suspect Parameter Number, is a unique numerical identifier for a specific parameter, such as engine coolant temperature or vehicle speed. It specifies what data is being transmitted within a message and is a key part of the J1939 standard for commercial vehicle communication. SPNs can also be used in diagnostic fault codes (DTCs) to pinpoint the exact component or sensor that is reporting an error.
An FMI code, or Failure Mode Identifier, is a two-digit number used in heavy-duty vehicle diagnostics (like those following the J1939 standard) to describe the specific nature of a fault. It works in conjunction with an SPN (Suspect Parameter Number) code, which identifies the component or parameter having the issue, with the FMI code providing the details on how it is failing. For example, FMI 0 could mean "data valid but above normal range," while FMI 2 could indicate an "erratic, intermittent, or incorrect" signal.
A DTC is both the SPN and FMI combined into one, an example would be SPN 100. FMI 31 or 100.31 which after looking at the list means oil pressure is seen without the engine running, would indicate a bad sensor or bad wiring.
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Fault Code Finder
About Fault Code Finder
Our Vision
Our Specializations
Our Specializations
It began as a fast, reliable reference for technicians, but quickly proved valuable for internal teams and customers as well. By providing accurate, easy-to-understand J1939 SPN/FMI information, Fault Code Finder helps users make smarter decisions, solve problems faster, and reduce unnecessary downtime—all while giving them greater confidence and control over their equipment.
Our Specializations
Our Specializations
Our Specializations
At Fault Code Finder, the focus is on heavy equipment diagnostics using the industry-wide J1939 protocol. We specialize in engines, hydraulics, electrical systems, and machine-control networks across construction, forestry, utility, and industrial machinery. Whether you're working with compact equipment or large production machines, you can rely on us for accurate SPN/FMI fault code information and dependable technical insight."