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Depending on where you live, your car could be required to undergo an annual or bi-annual inspection to make sure it’s not spewing too many toxic gases into the environment.

You’ll need to pass a smog check to renew your car’s registration, which you’ll need to carry valid insurance, and both of those are (almost) always important aspects of keeping your car street-legal. Although you don’t need to know the in-the-weeds details of smog checks, you should at least be familiar with what they are and why they’re required. Car Bibles’ editors have owned more than a handful of questionable cars over the years, many of which needed work to pass smog, so stick with us as we lay out the basics.

Let’s get rolling.

What is a smog check?

You may have heard about California smog regulations, but several other states have laws that require vehicles to pass inspections before registrations can be completed. Some states require vehicle components such as brakes and tires be inspected, while others include an emissions test. These checks, sometimes called smog checks, are designed to ensure that your vehicle isn’t releasing too many toxic chemicals into the atmosphere. 

The exact process varies from place to place and how old your car is, but a smog check generally includes having a technician look at your car’s engine, exhaust, and emissions controls to make sure they work, scanning the car’s computer to make sure it doesn’t have any fault codes, and running the car on a dyno (like a treadmill) with a sniffing device in the tailpipe. They may also check for vacuum leaks and test the gas cap to make sure it makes a good seal. 

A Mitsubishi Montero at a smog test station.
Some garages will be smog test only, while others can also do repairs. – Image: Andrew Collins

Where is a smog check performed?

States have different rules on where and how smog checks can be performed. In some cases, they can be done at a DMV station, but in most areas smog checks are able to be performed at a local shop that has been approved by the state. This can include dealership service centers, local mechanics, and other auto repair shops. The testing locations for some of the most populous states are listed below, but other states are similar.

New York

In the state of New York, vehicles can be smog checked at any state-registered inspection station. The station is required to post a sign with fees, and each vehicle must be inspected at least every 12 months.

California

In California, a vehicle can get a smog check at any DMV-authorized smog check station. The state offers an online tool to locate both smog check and smog repair shops at smogcheck.ca.gov.

Texas

Texas requires smog checks to be performed, but not all counties carry the requirement. Only 17 counties in the state require smog checks, which can be done at a licensed inspection station. Depending on the age of a vehicle, it could receive either an OBDII test if it’s newer than 1996 or an Accelerated Simulation Mode test if it’s 1995 model year or older.

Florida

Yee-haw! If you live in Florida, you’re probably already aware that smog checks are not required.

How often are smog checks required?

Some states require that vehicles pass inspections every year, while others have longer intervals. California, for example, requires that smog checks be performed every two years. It’s also worth noting that vehicles of a certain age are often exempt from smog checks because they were designed and built well before modern emissions testing and standards were created.

California also requires a used car to pass a smog check before it changes owners.

How much do smog tests cost?

The cost of your next smog check will depend on where you live and on the type of inspection you’re required to have. States like California work with private businesses to perform inspections, which means your local shop has a hand in the pricing. In most cases, an inspection will cost between $25 and $100, but remember that your costs may be higher or lower depending on what is being inspected.

Do brand-new cars require smog checks?

Vehicles of all kinds up to a certain age are required to have smog checks. In many places, new vehicles are required to pass a state smog check prior to sale, which is done at the dealer’s expense. If the car sits on a dealer’s lot for an extended period of time, a new smog check will need to be performed if the expiration date passes. The good news is that your new car will have recently passed smog, but the bad news is that you’ll be required to have another check performed when your state requires it (annually or another interval).

Are any vehicles exempt from smog checks?

Yes, older vehicles, some commercial vehicles, and others are exempted from smog checks. It’s important to note that the age and type of vehicle that meets exemption criteria differs from place to place. In California, the standards apply to all gas-powered vehicles manufactured after 1975.

A close-up of a BMW X6 M50i exhaust tip.
Smog checks make sure your emissions are on point. Photo: Tony Markovich

Tips for passing a smog check

If your car’s relatively new, stock, and maintained, you shouldn’t have anything to worry about when it comes to passing smog. But if your car’s a little older, or maybe not in perfect condition, here are some steps you’ll want to take to give the car its best chance at passing. Bear in mind, this is a combination of witchcraft and science:

  • Use quality gasoline from a Top-Tier gas station.
  • Make sure your air filter is relatively new — these are easy to change out on almost any car.
  • Consider running through a tank of gas with some fuel system cleaner in it. Seafoam, Redline SI-1, and Rislone fuel treatments tend to be favored by car enthusiasts.
  • Top off your fuel tank again before the test. Fresh gasoline is good.
  • Spend at least 30 minutes, maybe longer, driving at highway speed before you pull up for the smog check. Your car’s catalytic converter, essentially a chemical filtration system, works best when it’s hot.
  • Don’t shut your car down while you’re waiting in line for your smog test; you don’t want that cat converter to cool off.
  • Make sure your tires are well-inflated. That will minimize rolling resistance and could improve the car’s dyno performance.
  • If you’re not sure you’re going to pass, consider asking the technician for tips before having the car run through the test. You might also want to consider going to a small independent place which might have workers who are more familiar with older cars than the folks at a large corporate establishment.

What happens when you fail a smog check?

Failing a smog check means different things depending on where you live. In general, you’ll be given an assessment of where in the test your vehicle failed and given an opportunity to fix the issue. Because smog checks are usually performed by independent shops, you’ll likely be able to have the problem fixed right there and then. Or, you could take it home and try to fix it yourself. If you expect your vehicle to fail but want to keep it on the road, find a shop you can trust that does testing and repairs. Usually you’ll only have to pay for the smog check once if the same shop that tested you gets it to pass.

But do as much research as you can vetting shops online beforehand. If you tried all the “passing tips” above and still failed, your car might need some significant attention to run clean.

If you don’t fix it, you won’t be able to register your car. In many places, driving without an inspection sticker can result in a ticket and other penalties, so make sure you get over there!

Common reasons a car fails a smog check

Your vehicle could fail a smog check for a variety of reasons, some of which can be as simple as a bad sensor or fault code that needs to be cleared. Some common failure points include:

  • Air-fuel mixture is off
  • Bad spark plug or plugs
  • Dirty or old motor oil
  • Dirty engine air filter
  • Check engine light is on

Symptoms your car might fail a smog check

If your car failed a smog check because of a check engine light or bad sensor, you might not experience any symptoms, other than the warning light or error code. In many other cases, however, the issues that cause a failed smog check can also cause you to experience a drop in fuel economy, a rough idle, loss of power, or other issues with normal operation. 

What You Need To Know About Smog Checks
Use an OBDII scanner to check for codes in your car. Photo: Tony Markovich

The Glossary

Welcome to Bible school! 

Emissions

Emissions refers to the gases and byproducts created when a vehicle burns fuel to operate. This can include carbon monoxide, hydrocarbons, and more. Vehicles are required to be built with onboard mitigation systems that help reduce or contain the harmful emissions created while it’s in operation.

EVAP

A vehicle’s EVAP system is another name for its evaporative control system. EVAP systems are designed to prevent gas vapors from escaping into the surrounding environment. 

OBD2

OBD2, or onboard diagnostics, is a system of sensors and computers that monitor and control a vehicle’s operations. This can include emissions and engine metrics, such as the air-fuel mixture. The system generates error codes that correspond to various vehicle problems, which can be read using an OBD scanner tool

The Car Bibles Questionnaire

Q. What’s the difference between a smog check and a smog test?

A. In most cases, smog check and smog test both refer to the same thing. In some places, you will see a test only station, which means that the shop will test your car, but can’t do anything to fix the problems it uncovers. Smog test and repair stations can test your car and then help you repair any issues that came up during the process.

Q. Is it ok to drive with an EVAP leak?

A. We’re not going to tell you that it’s impossible, but we will tell you that it’s a terrible idea. You’ll not only be running the risk of letting your vehicle pollute the air more than it should, but you could be breathing in that pollution if the fumes enter the vehicle’s cabin. 

Q. Are smog checks biased against older cars?

A. This was a common concern as smog checks became more prevalent across the country, but it’s not completely accurate. It’s true that smog checks can seem harsh for aging vehicles, because they are typically more likely to have problems, but most states have age cutoffs, beyond which smog checks are not required. In some places, this corresponds with the ability to apply for an antique auto license plate, but it’s different from place to place, so be sure you understand your local regulations.

Video on Smog Checks

If you’re confused about what to buy to improve your vehicle’s smog check performance, you’re not alone. Car Bibles’ editors have grabbed a few of their favorite products to get your project started right. They include the BlueDriver Bluetooth OBD scanner, Hi-Gear catalytic converter cleaner, and Mechanix gloves.

Disclosure: Carbibles.com is also a participant in the Amazon Services LLC Associate Programs, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. Pages on this site may include affiliate links to Amazon and its affiliate sites on which the owner of this website will make a referral commission.

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