The bottom line: An emissions test, also called a smog test, measures the pollutants in your car’s exhaust. When you sell, the test is usually the buyer’s job at registration.
Four states make it the seller’s: California, Colorado, Georgia and Missouri. In 22 states there’s no testing program at all.
If you sell in one of those four, test the car before you list it, so there’s time to fix a fail.
If the car fails and the repair costs more than it’s worth, sell it as it is. Junk buyers take a car that failed, and Sell Car Advisor’s comparison tool gets you several instant offers at once.
Key Takeaways
- Same test: a smog test and an emissions test are the same inspection under two names.
- Check whose job it is: only four states put the certificate on the seller: California, Colorado, Georgia and Missouri.
- Fix the light first: with the check engine light on, a 1996 or newer car fails.
- Don’t clear the codes: a car whose computer was just reset reads “not ready” and is sent away.
- Won’t start? It can’t be tested, so sell it to a junkyard or a junk buyer instead.
- Sell it as is:
and
buy cars that failed, with no repairs first.
Automated assistant: general info, not legal advice
Answers come from our state paperwork data and published guides. Confirm anything binding with your state DMV.
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What Is an Emissions Test?
An emissions test checks that your car’s exhaust stays under the legal limits for carbon monoxide, hydrocarbons, nitrogen oxides and particulate matter.
Testing comes from the Clean Air Act of 1990, which required areas with poor air quality to run inspection programs. That’s why only some states and counties test.
Is a Smog Test the Same as an Emissions Test?
Yes. California and some western states say “smog test” and most other places say “emissions test”, but it’s the same inspection.
How Does an Emissions Test Work?
On a 1996 or newer car, the station plugs a scanner into the diagnostic port under the dashboard and reads the car’s computer. This is called an OBD-II test.
On an older car, a probe in the tailpipe measures the exhaust directly. Both kinds of test need the engine running.
You leave with a pass certificate or a report of what failed.
Do Sellers Have to Provide an Emissions Test?
In most states, no: the buyer has to pass the test before registering the car. In four states the certificate is the seller’s job:
| State | Whose job is the certificate? |
|---|---|
| California | Yes |
| Colorado | Yes, in most cases within the program area |
| Georgia | Yes, when both parties are in the 13-county testing area |
| Missouri | Yes, in the four affected areas: at the title transfer the seller provides the purchaser with a valid emissions compliance certificate or waiver, and the seller pays for the test. |
Rules differ by county in several states, so check yours before you list. Our list of state DMV websites carries the emissions line for all fifty.
How Much Does an Emissions Test Cost?
The fee, and how long a pass stays valid, depend on the state:
A fail costs more than the test. RepairPal puts the common emissions repairs at these national averages:
| Repair | National estimate, with parts at the manufacturer’s list price |
|---|---|
| Oxygen sensor | $440 to $523 |
| Spark plugs | $288 to $399 |
| EGR valve | $489 to $632 |
| Engine control module | $1,122 to $1,192 |
| Catalytic converter | $2,280 to $2,480 |
Get a repair estimate from RepairPal for your car, and set it against what buyers offer for the car.
How Do You Pass an Emissions Test?
- Fix the check engine light first. With the light on, a 1996 or newer car fails.
- Don’t clear the codes or disconnect the battery to put the light out. The car then reads “not ready” and can’t be tested.
What Happens If Your Car Fails an Emissions Test?
You can keep driving it until the registration is due, but the registration can’t be renewed until the car passes. Then you have four routes:
- Repair and retest. Fix the fault rather than clearing the code, then book the retest.
- Ask about repair help. Some states pay toward emissions repairs, or waive the test once you’ve spent a set amount.
- Sell it as is, where the certificate isn’t the seller’s job. Get a repair estimate, lower your price by about that much, and put the fault in writing. A signed statement that the buyer knew is your protection afterwards.
- Sell it to a junkyard or an online junk car buyer. Each seller-certificate state has its own rule for that sale.
A repair waiver doesn’t cover a sale. In California, a repair cost waiver from the Smog Check Referee postpones the certificate for a registration renewal only; a waived vehicle must be repaired before a change of ownership.
Repair help and waivers, where the state has them:
What If Your Car Won’t Start?
Then it can’t be tested: a car that won’t start gives no result at all, not a fail.
So there’s no certificate to get, no retest to book and no waiver to apply for. That leaves getting it running, which pays only if the repair is small, or selling it as it is.
In a state with no testing program, none of this applies, and our guide to selling a non-running car covers the rest.
Do You Need an Emissions Test to Junk a Car?
No, as long as the sale meets the state’s terms. Where the certificate is the seller’s job, these are the terms:
Tell each buyer the car failed or won’t start, so the offer accounts for it, and compare their offers through the comparison tool.
Compare instant offers before you accept one
Compare instant offers before you accept one
Frequently Asked Questions
What does “not ready” mean on an emissions test?
It means your car’s computer hasn’t finished its own checks since it was last reset, so the station has nothing to read. It isn’t a fail, but the station sends the car away.
It happens after the battery is disconnected, the codes are cleared, or the engine has had major work. The fix is to drive the car normally, on the highway and around town, until the checks finish. That’s also why clearing the check engine light before a test never works: the checks reset with it.
Article Update History
State seller requirements checked against official emissions testing program websites.
Originally posted and shared with our readers.
Sources
Emissions When Selling to a Dealer
"a dealer that resells the car has to provide a Smog Check passed within the past two years, so the certificate becomes the dealer's job when you sell to one" Accessed Sep. 15, 2026
Emissions Waiver and Ownership Change
"a repair cost waiver from the Smog Check Referee postpones the certificate for a registration renewal only; a waived vehicle must be repaired before a change of ownership" Accessed Sep. 15, 2026
"$440 to $523, oxygen sensor replacement cost; $288 to $399, spark plug replacement cost; $489 to $632, eGR valve replacement cost; $1,122 to $1,192, engine control module (ECU) replacement cost; $2,280 to $2,480, catalytic converter replacement cost" Accessed Sep. 11, 2026
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