GUIDE / OBD-II
Readiness is not the same as no fault
Readiness shows whether supported diagnostic tests have completed since a reset. Clearing codes or disconnecting the battery may reset it. An incomplete monitor does not prove a component failure; a complete monitor does not certify the whole vehicle. Enabling conditions and drive cycles vary by vehicle. Follow the manufacturer procedure and local inspection rules, not an arbitrary mileage target.
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Scan worksheet →Source-backed code explanations
Sources and interpretation
Read the meaning first, then follow the cited manufacturer pages. The explanations and vehicle-specific examples have different scopes; verify the exact application before using a repair instruction.
- On-Board Diagnostic Test Reference — Section C, Readiness monitor standards ↗
California Bureau of Automotive Repair
California reference explains readiness self-tests, vehicle-specific enable conditions and the effect of battery disconnection or repairs. Supports using manufacturer drive-cycle instructions; its inspection tables and exceptions apply only within the California program.
- Performing Onboard Diagnostic System Checks as Part of a Vehicle Inspection and Maintenance Program — EPA420-R-01-015, June 2001 ↗
U.S. Environmental Protection Agency
Historical US report, Readiness Status sections, printed pages 10–15: evaluated/not-evaluated status, manufacturer-dependent enabling conditions, reset effects and why incomplete status alone does not establish an emissions defect. Its old monitor inventory, test allowances and suggested driving duration are not current worldwide guidance.