About Iron Fault

Iron Fault is a free fault code explainer for diesel trucks, tractors and heavy equipment. Paste a J1939 SPN/FMI code and get a plain-English meaning, how serious it is, likely causes and what to check first — plus where to get the official manual legally.

How we write content

Every explanation is written in our own words from general diesel knowledge. We don't copy OEM manuals or proprietary code databases. Generic J1939 failure modes (FMI 0–31) are described in plain language. Code-specific behavior varies by manufacturer, model year and software, so always confirm with OEM service information.

Manuals

We never host copyrighted manuals. We point you to the manufacturer's own portals and authorized dealers.

How we make money

Lookups are free. In the future we may earn commissions from clearly labeled affiliate links. No affiliate links are active today.

Corrections

Spotted a mistake? A corrections form is coming soon.