Emissions Testing in Missouri

Who Needs an Emissions Test or Smog Check

Certain light duty vehicles must undergo emissions testing in designated areas. Gasoline vehicles from model year 1996 and newer and diesel vehicles from model year 1997 and newer with a gross vehicle weight rating of 8,500 pounds or less are subject to inspection if registered in specified counties. Exemptions may apply based on age, weight, fuel type or mileage.

How Often Tests Are Required

Emissions tests generally occur every two years in areas where they are required. Vehicle owners receive notice approximately 60 days before registration expiration. Even model year vehicles are inspected in even years, odd model year vehicles in odd years. Testing may also be required at title transfer or new registration.

Where Emissions Testing Is Required

Testing is required only in certain parts of the state. The Gateway Vehicle Inspection Program covers St. Louis City, St. Louis County, St. Charles County and Jefferson County. Other areas are exempt. Requirements vary by location and vehicle registration area.

What Happens During the Test

During a test at an official Gateway Vehicle Inspection Program station, a technician connects to the vehicle’s OBD‑II system to check emissions readiness monitors and emissions control status. The test may include visual inspection and tailpipe sampling if needed. Technicians verify emissions systems integrity and diagnostic data to ensure compliance. A pass generates a report and windshield sticker, valid for registration purposes.

Areas in Missouri That Require Emissions Testing

Emissions testing requirements differ across Missouri. Only specific parts of the state require emissions testing under state law. Several of the major cities where listings appear, such as St. Louis, Springfield, St. Charles, Kansas City, Columbia, Lee’s Summit, Florissant, St. Peters, Blue Springs and St. Joseph are included in the directory for convenience. Note though that only the St. Louis metropolitan area (including St. Louis City, St. Louis County, St. Charles County and Jefferson County) requires emissions inspections mandated under the Gateway Vehicle Inspection Program. Other cities like Springfield, Kansas City, Columbia, Lee’s Summit, Florissant, St. Peters, Blue Springs and St. Joseph are exempt from emissions testing under state rules. This means that at emissions testing locations in Missouri, many of the listings outside the St. Louis area serve customers who may need inspections based on registration or may serve safety inspections only. Vehicle owners should confirm requirements before visiting any station.

How the Emissions Test Works in Missouri

An emissions testing visit typically lasts 15 to 30 minutes. Bring the vehicle’s registration and your ID. First, check in at the station and confirm whether emissions testing is required. The technician connects to the OBD‑II port, checks readiness monitors and may perform a tailpipe test or visual inspection of emissions equipment if needed. Common failure reasons include the check engine light being on, incomplete readiness monitors, or malfunctioning emissions components. If the vehicle fails, you receive a failure report and can return for one free retest within 20 business days at the same station. Costs vary by station, though the state caps the testing fee. If you fail and cannot repair in time, registration may be delayed. Allow time for necessary repairs and retesting.