What the Database Contains
The lookup index covers fault code pages, SPN topic pages, FMI reference pages, symptom pages, glossary terms, system pages, diagnostic guides, and tool pages. Each record in the index must be connected to a verifiable source before it is included in search results or the sitemap.
Fault code records include source-checked Bendix EC-60 ABS/ATC/ESP codes, J1939 SPN/FMI educational pages, ELD malfunction and data diagnostic event codes from FMCSA sources, and OEM-context pages for major engine and brake suppliers. Records that lack a traceable source document, conflict with source data, or do not pass publishing review are excluded.
Reading a J1939 Fault Message
Most modern heavy-duty trucks send diagnostic data over a J1939 data link. A fault message combines an SPN — the parameter being reported — with an FMI that describes the type of abnormal condition the module detected. FMI 3 and 4 mean signal voltage high and low; FMI 5 and 6 mean current low and high; FMI 9 means the ECM stopped receiving an expected message update from another module on the network.
Source Address (SA) identifies which module generated the fault. The same SPN/FMI pair can appear identical on a driver's display whether it was reported by the engine ECM, the transmission controller, the ABS module, or the instrument cluster — but those are completely different diagnostic paths. If your diagnostic tool shows source address alongside the SPN and FMI, note it. It changes where you start.
Active Codes vs. Stored Codes
An active fault means the ECM is detecting the condition right now. A stored or inactive code means the condition was detected at some point but is not currently present — the signal returned to range, the module recovered, or the fault was intermittent. Active codes take priority, but stored codes provide context, especially for recurring or intermittent concerns.
Before clearing anything, record the full code list, which codes are active vs. stored, all warning lamps and derate conditions, recent operating conditions, and vehicle mileage and engine hours. Occurrence counts and timing data that some OEM systems maintain disappear when codes are cleared — and intermittent faults are much harder to diagnose without that history.
FAQ
Does the search send data to a server?
No. The page loads a static JSON index generated at build time and filters it entirely in your browser. No query, no vehicle data, and no personal information is transmitted anywhere.
What can I search for?
SPN number, FMI number, OEM code, manufacturer, system, component, symptom, glossary term, or any keyword. Partial matches work — typing 'wheel speed' will surface wheel speed sensor fault records, related symptom pages, and glossary entries that contain the term.
What does 'source-backed' mean on this site?
A source-backed record is tied to a specific, identifiable official document — an OEM service bulletin, a government database, or a registered standard reference. Records without a traceable source are written with lower-confidence labels and are excluded from search and the sitemap. The source registry lists every document referenced on this site.
Why does the same SPN/FMI number sometimes mean different things on different trucks?
J1939 SPN/FMI codes describe a parameter and a failure mode, but the thresholds, calibration-specific triggers, and OEM responses vary by engine family, model year, ECM software version, and emissions tier. A SPN 3364 FMI 1 on a Cummins ISX15 EPA13 follows different inducement logic than the same code on a GHG17 Detroit DD15. The SPN/FMI pair is a starting point — the OEM's specific service documentation for the exact engine serial number and calibration is the final authority.
Why are some codes I searched for not in the results?
Records are excluded if they cannot be tied to a verifiable source, if the source document is no longer accessible, or if the record did not pass internal publishing review. Older OEM codes with no traceable public documentation, manufacturer-specific codes that are not publicly published, and records with conflicting source information are not indexed.
I found my code here. What do I do next?
Use this site as context, not a repair instruction. Record the full code — SPN, FMI, active or inactive status, warning lamps, derate state, related codes, and recent operating history — then use OEM service information, the appropriate manufacturer diagnostic software, and a qualified technician to complete the process. Pages on this site explain terminology and first-check guidance but do not replace OEM repair procedures.