Check the engine light and fix any diagnostic trouble codes
Make sure the gas cap is tight and in good condition
Change the oil if it is dirty or overdue
Replace a clogged air filter
Replace worn spark plugs and ignition components
Inspect and repair vacuum leaks
Warm up the engine before the test
Drive the car for at least 15 to 30 minutes before testing
Keep the fuel tank between one-quarter and three-quarters full
Use the correct fuel grade
Add a fuel system cleaner if appropriate
Repair exhaust leaks
Make sure the catalytic converter is working properly
Check oxygen sensors and replace if faulty
Ensure the battery is fully charged
Verify the tires are properly inflated
Avoid disconnecting the battery right before the test
Complete all required drive cycles after repairs
Confirm readiness monitors are set
Fix any EVAP system issues
Test the car before the official emissions inspection
Bring the vehicle to a mechanic if problems persist