A stored code tells you what a control module detected. It rarely proves which part failed.
The code directory helps classify a signal without turning a stored DTC into a failed-part conclusion.
Follow the sequence, stop when evidence changes the path, and verify the exact vehicle information before acting.
These definitions are standard generic OBD-II descriptions. Manufacturer-specific codes can differ and require exact documentation.
IAR can organize every DTC family. Definitions are published only when a standard or exact manufacturer source supports them.
The current library contains 43 reviewed generic P-code pages. Each definition links to the primary standard record; diagnostic advice remains general unless exact applicability is shown.
Review the source library →The same code text can change by make, module, model year, or implementation. IAR does not publish an enhanced definition until its manufacturer, module, applicability, and source are recorded.
Choose a manufacturer →Code-family and generic-definition claims are tied to the current SAE diagnostic-trouble-code standard record. Vehicle test thresholds, circuit layouts, and enhanced code meanings still require exact manufacturer information.
A monitor can be not ready without proving a component failed. Learn what ready, not ready, and not applicable mean before clearing evidence or preparing for an emissions inspection.
Understand why recent battery work, code clearing, operating conditions, or vehicle-specific behavior can leave a monitor incomplete.
Open readiness guide →Exact monitor enable criteria differ by vehicle. IAR keeps the general concept separate from manufacturer procedures and local inspection rules.
Review source boundaries →Code availability and interpretation depend on the vehicle, module, and scan-tool access. Use manufacturer service information for enhanced and manufacturer-specific codes.