Fault codes & diagnostics•Practical, driver-friendly explanations
BigRigFaults
Clear explanations for truck fault codes: what they usually mean, what to check first, and common fixes. Built for drivers, fleet owners, and technicians who want answers fast.
Coverage
SPN/FMI • OBD • OEM
One format doesn’t fit all. We keep it practical.
Pages
Growing library
Adding more codes, brands, and problems regularly.
Goal
Faster diagnosis
Start with quick checks before swapping parts.
Search fault codes
Search by SPN/FMI (e.g. 5394 31 or SPN 5394 FMI 31), OBD codes (e.g. P0420), or keywords. Prefix works too (type 5 to see codes starting with 5).
Brand
Engine
Fault Codes
SPN/FMI, OBD, manufacturer codes with quick checks.
Browse →
Problems
Common symptoms and likely causes across systems.
Browse →
Brands
Freightliner, Volvo, Kenworth, and more.
Browse →
Engines
Cummins, Detroit, PACCAR and more.
Browse →
What you get
- Plain-English breakdown of what the code usually means.
- Quick checks so you can confirm before replacing parts.
- Common fixes based on typical real-world failures.
Safety note
This site is informational. Always confirm with your OEM service manual and proper diagnostic tools. If you’re dealing with a breakdown on-road, contact roadside service.
Want a code added?
If you have a code that’s missing or an incorrect description, contact us and include the engine/brand and exact code format (SPN/FMI, OEM, etc.).