An emissions test in Missouri costs up to $24. That’s a state-set maximum, and it applies at every licensed Gateway Vehicle Inspection Program station in the St. Louis area.1U.S. Environmental Protection Agency. Missouri Code 10 CSR 10-5.381 – Onboard Diagnostics Motor Vehicle Emissions Inspection Stations are free to charge less, but most charge the full amount. If you also need a safety inspection, that’s a separate visit and a separate fee, capped at $12 for cars and trucks or $10 for motorcycles, so the practical ceiling for both is around $36.2Missouri State Highway Patrol. Motor Vehicle Inspection FAQs
What the $24 Covers
You pay the fee whether your vehicle passes or fails. It covers the technician’s time and the OBD-II scan itself, not the outcome. The station posts the price visibly, and each location decides which payment methods it takes, so bring cash as a backup.
The scan takes a few minutes. A technician plugs a diagnostic tool into the port under your dashboard and reads data from your vehicle’s onboard computer. There is no tailpipe probe. The system checks stored trouble codes and confirms that the emissions-related self-tests, called readiness monitors, have completed.
If your vehicle fails, one re-inspection at the same station is free, provided you return within 20 business days.1U.S. Environmental Protection Agency. Missouri Code 10 CSR 10-5.381 – Onboard Diagnostics Motor Vehicle Emissions Inspection Weekends and holidays don’t count, so you have roughly four calendar weeks. Go to a different station, or miss the window, and you’ll pay another $24.
Results are only valid for 60 days (120 days for dealers), so don’t test too far ahead of your registration renewal or you’ll have to do it again.3Missouri Department of Revenue. Motor Vehicle – Additional Help Resource
Where the Fee Applies
Emissions testing is required only for vehicles registered in four jurisdictions: St. Louis City, St. Louis County, St. Charles County, and Jefferson County.4Gateway Vehicle Inspection Program. Does My Vehicle Need a Test Register your vehicle anywhere else in Missouri and you owe nothing for emissions. Safety inspections still apply statewide.
Franklin County used to be part of the program. A 2022 rule change removed it, and vehicles registered there are now exempt unless at least 51% of their annual miles are driven inside the four remaining jurisdictions.1U.S. Environmental Protection Agency. Missouri Code 10 CSR 10-5.381 – Onboard Diagnostics Motor Vehicle Emissions Inspection
The requirement follows where the vehicle is registered, not where it was bought. If you move into a testing county from elsewhere in the state, your next registration renewal will require a passing emissions result. Leased, rented, or out-of-area vehicles that spend more than half their annual mileage inside the testing area also need the test.5Legal Information Institute. Missouri Code 10 CSR 10-5.381 – Onboard Diagnostics Motor Vehicle Emissions Inspection
When You Don’t Have to Pay Anything
Even inside the testing area, several categories of vehicle are exempt. If any of these fit, you skip the $24 entirely.
- Gas vehicles with a 1995 or older model year, and diesel vehicles with a 1996 or older model year.4Gateway Vehicle Inspection Program. Does My Vehicle Need a Test
- New, unused vehicles in their first model year with fewer than 6,000 miles at original sale.1U.S. Environmental Protection Agency. Missouri Code 10 CSR 10-5.381 – Onboard Diagnostics Motor Vehicle Emissions Inspection
- Vehicles not yet titled or registered, for four years after their model year, if they have fewer than 40,000 miles. Requires a Mileage-Based Exemption Request filed with the Department of Natural Resources.3Missouri Department of Revenue. Motor Vehicle – Additional Help Resource
- Any vehicle driven fewer than 12,000 miles between biennial safety inspections. Same DNR form, plus odometer readings from both safety inspections.3Missouri Department of Revenue. Motor Vehicle – Additional Help Resource
- Vehicles powered exclusively by electricity, hydrogen, or solar power, and plug-in hybrids. Standard hybrids with a gas or diesel engine still need testing.4Gateway Vehicle Inspection Program. Does My Vehicle Need a Test
- Vehicles with a manufacturer’s gross vehicle weight rating over 8,500 pounds.1U.S. Environmental Protection Agency. Missouri Code 10 CSR 10-5.381 – Onboard Diagnostics Motor Vehicle Emissions Inspection
- Motorcycles, motortricycles, vehicles with historic plates, school buses, tactical military vehicles, and specially constructed or kit vehicles.3Missouri Department of Revenue. Motor Vehicle – Additional Help Resource
Low-mileage exemptions aren’t automatic. Apply to the Department of Natural Resources before you try to register the vehicle, or the Department of Revenue will still expect a passing test.
What It Costs If Your Vehicle Fails
A failed test doesn’t add fees at the station beyond the original $24, but repairs can turn into the real expense. You can’t renew your registration without a passing result, and Missouri only allows a 30-day grace period past your expiration date for driving the vehicle while you reset readiness monitors after repair. The standard $5 late-renewal penalty still applies.3Missouri Department of Revenue. Motor Vehicle – Additional Help Resource
If repairs won’t get the vehicle to pass, Missouri offers a waiver, but only after you’ve spent a minimum amount trying:
- $450 in qualifying repair costs when work is done by a licensed technician.
- $400 in qualifying parts when you do the work yourself.
- $200 in qualifying repairs for owners on public assistance or disability.1U.S. Environmental Protection Agency. Missouri Code 10 CSR 10-5.381 – Onboard Diagnostics Motor Vehicle Emissions Inspection
There’s also an estimate-based waiver available when a diagnosis shows the parts and labor to fix the failure would exceed $450.6Gateway Vehicle Inspection Program. Forms, Waivers and Extensions Keep every receipt: waivers depend on documenting what was done and how much you paid.
Extra Times You’ll Pay $24
The biennial cycle isn’t the only trigger. Any title transfer inside the testing area requires a fresh emissions inspection, no matter where you are in the two-year rotation.4Gateway Vehicle Inspection Program. Does My Vehicle Need a Test Sell a car with an even model year in an odd calendar year, and the buyer will still need a passing test to register it.
Missouri doesn’t dictate which party pays for that inspection. Sellers who show up with a recent passing result tend to close deals faster; buyers who require testing before purchase avoid ending up with a vehicle they can’t register. Either way, the $24 is on the table.
The biennial schedule itself follows model year. Odd model years test in odd calendar years, even in even. A 2020 vehicle tests in 2024, 2026, 2028. The Department of Revenue mails your renewal about 60 days before your plates expire, which is roughly when you should schedule the inspection.4Gateway Vehicle Inspection Program. Does My Vehicle Need a Test
One last cost consideration: don’t head to the station immediately after a repair that cleared diagnostic codes or required disconnecting the battery. The vehicle’s readiness monitors reset when that happens, and too many incomplete monitors is an automatic fail even when the underlying problem is fixed. Drive the car normally for a week or so first, or you’ll burn your free re-inspection on a preventable failure.