• Kenneth Powell

Do You Have to Pass a Smog Test in Missouri?

It should come as no surprise that the transportation sector accounts for more than 55% of all nitrogen oxide emissions in the country. Unfortunately, NOx gasses are the leading causes of acid rain and smog, which lead to lung problems as well as eye and nose irritation. As a result, smog tests have become the norm in many states, especially in metropolitan areas. But are they a requirement for vehicles in the state of Missouri, and if so, what can a driver do to prepare for a smog test?

Does Missouri Require a Smog Test?

Does Missouri Require a Smog Test?

The state of Missouri requires smog checks and emissions tests for vehicles in metropolitan areas. These areas include St. Louis City and County, Jefferson County, St. Charles County, and Franklin County. However, only a certain category of vehicles needs to be tested. More specifically, diesel vehicles manufactured in 1997 or later and gasoline vehicles manufactured in 1996 or later and weighing less than 8,500 lbs. need to pass a smog check.


Vehicles that fall under at least one of the following categories are exempt from having to pass a smog check:

● Vehicles manufactured in even model years whose registration expires in odd calendar years.

● All types of trailers.

● Vehicles manufactured in odd model years whose registration expires in even calendar years.

● Dirk bikes, motorcycles, and motor tricycles.

● Motor vehicles that were sold during the vehicle’s model year or the following year that have no more than 6,000 miles on their odometer during the sale.

● RVs and motor vehicles that weigh over 8,500 lbs.

● Vehicles for sale as salvage, junk, or for rebuilding.

● Title Only vehicles.

● Low-speed gasoline vehicles.

● Vehicles that are registered with the Department of Transportation for use in interstate commerce.

● Vehicles bought and sold between dealers.

● Electric, solar power, hydrogen, or dual-fueled vehicles that use any other fuel than diesel, gasoline, or E85 and E10.

● Vehicles with the school bus, street rod, or shuttle bus plates.

● Plug-in electric-drive vehicles.

Missouri also offers exemptions for drivers depending on special circumstances. For instance, vehicle owners might be eligible for a mileage-based exemption if their vehicles meet the criteria:

● Motor vehicles that are driven less than 12,000 miles between the mandatory two-year safety inspection

● New vehicles that are untitled during the 4-year period after the model year and that weren’t driven for more than 40,000 miles by the time of the first safety inspection.

Additionally, owners who live in one of the areas that require smog testing but have been away from home for a minimum of 24 months prior to the test can apply for an out-of-area waiver. They’ll have to submit a notarized request to the Department of Natural Resources in order to apply.

What If the Vehicle Fails the Smog Inspection?

If a vehicle doesn’t pass the smog inspection, the owner will receive:

● A repair information sheet indicating the repair location and a performance report.

● A Vehicle Information Report certifying the vehicle failed the inspection and the areas it did not pass.

● A list of the nearest emissions testing locations. These locations also have emissions-repair technicians who are able to calculate the repair expenses the owner might need to pay.

It’s important to mention that when a vehicle doesn’t pass the inspection, the owner has 20 business days to get it retested to be eligible for a free retest. Keep in mind that the driver doesn’t have to return to the same testing location to take advantage of the offer.

Tips to Pass the Emissions Test

Nobody wants their vehicle to fail the emissions test, especially since it results in wasted time and money. Here are a few tips that will help owners ensure their vehicle passes the test:

● Vehicles that have their Check Engine lights on will not pass the test. To fix this issue, drivers need to make sure that the gas cap is closed tightly and not broken. They should also keep the sealing surfaces clean, so they can connect as intended.

● Check if the vehicle’s oil is dirty and replace it if necessary.

● Drive the vehicle for at least 10 minutes before the test to ensure an accurate reading.

● Vehicle owners need to follow the recommended maintenance schedule. Most mechanical issues that cause vehicles to fail the test can be fixed during routine check-ups.

● If the vehicle’s on-board diagnostic system is showing trouble codes, drivers need to have it checked by a certified technician. Just clearing the codes won’t work, as test personnel will know.

● Research the vehicle manufacturer’s recalls and warranties before getting any repairs, as some of them could be covered by the manufacturer.

● Inspect the vehicle’s belts and hoses for wear and replace them if necessary.

● If the vehicle’s battery is new, owners should drive the vehicle for a few days before getting a test to allow the on-board diagnostics system to reset.

● Drivers need to contact a technician if the vehicle misfires when idling.

Other than the smog test, a motorcycle rider also needs to determine if motorcycles need turn signals in Missouri.

When it comes to driving motorcycles, the accident risk is higher. It's important to wear safety gear and know the traffic rules such as whether or not lane splitting is illegal in Missouri.

For other questions regarding motorcycle inspections, consult an experienced attorney from a motorcycle accident law firm in St Louis today.