A trouble code is a starting point, not a verdict. When your check engine light comes on and an OBD2 scanner pulls a code, it tells you which system triggered the fault, not which part failed or what it will cost to fix. Every entry in this library explains what the code means, which systems it involves, what commonly causes it, and what a scanner can and cannot confirm on its own.
OBD2 codes fall into four categories: powertrain (P), body (B), chassis (C), and network (U). Each category covers different vehicle systems, from the engine and transmission to the ABS and airbag modules. Use this library to understand what you’re actually looking at before you spend money at a shop or order parts you might not need.