Short answer: a scanner can show readiness status. It cannot force the vehicle to complete its tests.
What readiness monitors are
The OBD-II system runs emissions-related self-tests for systems such as the catalyst, evaporative emissions, oxygen sensors and exhaust-gas recirculation where applicable. A monitor marked ready has completed. “Not ready” or “incomplete” means it has not.
Why monitors reset
- Codes were cleared with a scan tool
- The battery was disconnected or lost power
- Vehicle memory was reset during repair
- The test conditions have not occurred yet
This is why clearing a check-engine light in the parking lot before an inspection is usually counterproductive.
What is a drive cycle?
A drive cycle is the combination of temperatures, speeds, loads, stops and time a vehicle needs to run its monitors. There is no universal ten-minute recipe. Some tests need a cold start, a particular fuel level or sustained cruise conditions.
Can one monitor stay incomplete?
Yes. The evaporative monitor is a common holdout because it needs narrow conditions. Inspection rules vary by location, model year and fuel type, so check the current requirements where the vehicle will be tested.
Readiness and used cars
Several incomplete monitors may mean codes were recently cleared, but it is not proof of deception. Battery service and legitimate repairs can produce the same status. Ask why, look at service records and scan again after an adequate drive.
Permanent codes are different
Permanent codes cannot be erased manually. The vehicle clears them after it verifies the repair. Some inspection programs check permanent codes on supported model years in addition to readiness.
Quick questions
Can I pass with one monitor not ready?
That depends on the inspection program, model year and monitor. Check the current local rule rather than relying on a generic answer.
How long does readiness take?
It may take one correct drive cycle or several days of normal driving. The exact conditions are vehicle-specific.
Will disconnecting the battery clear readiness?
It usually resets monitor status and can erase useful diagnostic history.
Technical reference: California BAR readiness-monitor explanation. Inspection standards vary by jurisdiction.