In Missouri, testing emissions on vehicles is required for certain vehicles. All new vehicles will need to pass an emissions test before they can be registered, unless they are stated vehicles that are exempt.

Vehicles that need to pass an emissions test are required when the following applies:

  • A vehicle that has a model year of 1996 of newer and are gasoline powered. It must have a gross vehicle weight rating of 8500 pounds or less.
  • A vehicle that has a model year of 1996 or newer and is powered by diesel, and has a gross vehicle weight rating of 8500 pounds or less.
  • The vehicle is registered to going to be registered in St. Louis City, St. Louis County, St. Charles County, Franklin County, or Jefferson County.
  • If there is a title transfer of the vehicle.

Odd model year vehicles are required to be emissions inspected in odd calendar years and even model year vehicles are required to be inspected in even calendar years. A valid test is required to complete a used vehicle purchase registration, a currently owned registration renewal and to reinstate a suspended registration.

Used car dealers are required to provide the purchaser with a valid emissions inspection for any vehicle they sell, or to inform the purchaser they have 10 days or 1000 miles to emissions test the vehicle and if it fails, return it to them, to allow them to perform the emissions repairs needed (at no charge to the purchaser) to get it to pass or to come to some other mutual agreement.

A private seller is required to document to the purchaser the vehicle met emissions inspection compliance just prior to selling the vehicle.

Source: http://www.dmv.com/mo/missouri/emissions-testing