Diagnostic guides
Practical, narrative guides for reading scanners, understanding P/B/C/U letters, and decoding J1939 SPN/FMI on heavy trucks.
How to read an OBD-II scanner: a beginner’s guide
Learn what an OBD-II scanner shows, how to connect it safely, and how to turn codes into a sensible diagnosis—without clearing faults too early.
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P/B/C/U codes explained: what each letter means
Decode the first letter of an OBD-II trouble code—powertrain, body, chassis, or network—and use it as a smarter starting point before you buy parts.
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SPN/FMI for heavy trucks: understanding the J1939 system
Learn how heavy-duty diagnostic trouble codes use Suspect Parameter Numbers and Failure Mode Identifiers on the SAE J1939 network—and how that differs from passenger-car OBD-II letters.
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