How can I tell if my vehicle is ready for an emissions test (smog check)?

Use the Code Reader's LED indicators as a quick check: a green LED means all monitors have run and no DTCs are present, indicating the vehicle is likely ready to pass an emissions test. A yellow LED means a pending code exists or some monitors have not completed testing, and readiness depends on local regulations. A red LED means DTCs are present and the vehicle is not ready for an emissions test until the underlying problem is repaired. (Page 24–25)