In the state of Missouri, it is required by law that your vehicle must pass an emissions inspection. For drivers in the St. Louis region, the state’s Gateway Vehicle Inspection Program is designed to improve urban air quality. The inspection, refered to as emissions testing or state inspections, will check the vehicle’s computer and OBD-II (Onboard Diagnostics) system for any emissions-related trouble codes that have been stored. Usually, a trouble code will result in an illuminated Check Engine lamp, but not always. Any diagnostic trouble codes that are emissions-related will need to be repaired before the vehicle can pass emissions testing.
If your vehicle fails the safety inspection, you have 20 business days to have the problem repaired, then retested at a certified inspection station in order to avoid a second inspection fee. If you go past the 20-day mark, you will have to pay for the inspection a second time. The State of Missouri offers no waivers for failed inspections; if your vehicle cannot pass, you will not be able to register it with the state. You will also receive one re-inspection free of charge within the 20-day window