Example code
P0301 PSystem family: Powertrain 0Generic SAE / OBD-II definition 3Subsystem: Ignition or misfire 01Specific fault: Cylinder 1Reading the structure
Start with the complete code
A diagnostic trouble code is a structured reference. Read every character, including any suffix reported by the scan tool, before deciding what the code means.
1. Identify the family letter
P is powertrain, B is body, C is chassis and U is network communication.
2. Check whether it is generic
A second character of 0 usually indicates a standard SAE/OBD-II definition. Other values can indicate manufacturer-controlled or enhanced definitions, so the vehicle make, model and reporting module matter.
3. Read the subsystem and fault number
The remaining characters narrow the system and the particular condition detected. They identify evidence recorded by a control module; they do not automatically identify a failed part.
4. Preserve suffixes and context
Some tools add failure-type suffixes, status information or freeze-frame data. Record these details together with the module name, mileage, symptoms and battery voltage.
Search the fault-code database