What Is an Emissions Test? How It Effects Your Vehicle

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Have you ever pulled into your mechanic's shop to see a sign that says "Emissions Testing Offered Here" and wondered, "what is an emissions test?" Don't worry. You aren't the only one.

Because this test can vary from state to state, it can be confusing. You may even have recently moved from a state that didn't require vehicle emissions testing.

Before you get worried, there is nothing for you to do other than dropping your car off at the repair shop. A trusty mechanic will take care of the rest.

What Is an Emissions Test?

​Well, what is an emissions test? To put it simply, the answer to "what is an emissions test?" is that it is a smog test. Before we delve too far into the answer to "what is an emissions test?" you probably want to know what smog is.

If you have ever been to a big city where there is a lot of traffic, you have probably noticed it seems a little hazy. This haze is smog. There are two different types of smog: sulfurous smog and photochemical smog. The first comes from the burning of fossil fuels that contain sulfur, like coal, for example.

When your car is getting an emissions test, they are looking for many pollutants such as carbon monoxide, non-methane organic gases, formaldehyde, and nitrogen oxide. This type of smog is known as photochemical smog.

All of our vehicles put off emissions and to make sure they are only putting off the fixed amount you may be required by your county or state to have your vehicle tested annually. The Environmental Protection Agency (EPA) sets the amount of emissions your vehicle can produce.

What does an emissions test entail?

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If your vehicle is from the year 1996 or newer, the test itself is pretty straightforward.

When you take your car to your mechanic, they will hook it up to a diagnostic computer. Once your vehicle is hooked up, the machine will indicate to the technician whether your car is producing more than the fixed amount of pollutants.

For any vehicle made before 1996, your technician may do a visual inspection of your vehicle's exhaust system. They may also put your vehicle on a dynamometer, more commonly referred to as a dyno. This machine helps simulate driving allowing the mechanic to analyze your exhaust emissions manually.

Because these testing requirements vary from state to state, you must check your local and state regulations.

Can Your Car Fail an Emission Test?

​Your car is running perfectly fine, so that means you pass the test, right? Unfortunately, this isn't always the case.

Like every other test you have taken in your life, your vehicle can either pass or fail an emissions test. When your mechanic hooks up your vehicle to their diagnostic computer, it will tell them whether your car will pass or fail.

Making sure to maintain your vehicle's engine properly can help decrease the likelihood that your car will fail an emissions test. Proper maintenance can start with something as simple as making sure to change your oil and filters.

Signs your vehicle may fail

​A significant indicator that your car will fail an emissions test is your check engine light is on. If this light comes on, check with your mechanic to have a diagnostic test done to indicate what is going on with your car's engine.

You could attempt to clear this code yourself if you have a diagnostic tool such as this. Clearing the system yourself may not work, though. More often than not, once the vehicle is hooked up to the diagnostic computer, the code will reappear.

Reasons your car may fail

​Now that we know what the answer to "what is an emissions test?" is, there are some reasons why your vehicle may fail.

If your car does fail an emissions test, don't get discouraged. A failure can come from any number of things ranging from a loose gas cap to significant engine problems.

Loose or leaking gas cap

This problem is one of the most straightforward reasons why your car could fail an emissions test. If you believe your gas cap is leaking, you can easily replace it with a sealing one yourself.

A loose or leaking gas cap may tell your computer that your Evaporative Emission Control System (EVAP) is not working correctly. When this system stops working correctly, gas vapors can escape from your gas tank. It's best if you can find the best locking gas cap.

Rich air-fuel mixture

Have you ever gotten behind a vehicle that smells like rotten eggs? That is a big sign that their air-fuel combination is not right, and their car is running too "rich."

In simple terms, this means that a vehicle is getting too much fuel and not enough air. The cause of a rich air-fuel mixture can range from bad injectors to a misfunctioning oxygen sensor.

Running a vehicle with too costly of an air-fuel combination can cause a lot of damage to your car, including damaging your catalytic converter.

Faulty oxygen sensor

Of all of the parts of your car's emissions system, the oxygen sensor is the most important. The oxygen sensor helps monitor the amount of oxygen in your car's exhaust fumes and relays that information back to your vehicle's computer.

Because of its location in your exhaust pipe, this sensor can sometimes get covered in soot, making it difficult to read your exhaust fumes correctly. Once the sensor can no longer appropriately read the fumes, it will turn on your car's check engine light.

If you have noticed your fuel economy getting worse, black smoke coming out of your tailpipe, or hesitation or stalling, these are signs that you may have a faulty oxygen sensor.

Damaged catalytic converter

Your catalytic converter sits next to your muffler in your car's exhaust system. It is made of a mixture of metals, set in a honeycomb pattern, that helps dilute the pollutions that come out of your exhaust pipe. When it becomes damaged, it can cause you to fail an emissions test.

Several things can damage your catalytic converter, including unburned fuel, coolant leaks or oil.

Unburned fuel can cause the honeycomb pattern in the catalytic converter to melt because of the extreme heat it produces. Coolant leaks can contaminate the metals, making them unable to convert the exhaust fumes accurately.

If your vehicle starts to consume too much oil, this can also cause significant damage to the catalytic converter. It causes problems similar to a coolant leak.

What to Do If Your Car Fails

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​The first thing you are going to want to do if your vehicle does not pass is to find out why. Once you figure out the problem, you can have your mechanic fix it for you.

If you are capable, you can also adjust the problem yourself. You will have to have your vehicle tested again.

Should you get a second opinion?

​Because this is a diagnostic test, going to a second garage to have an emissions test performed is more than likely going to be a waste of your time.

Are There Exceptions for Emissions Testing?

​Depending upon what state you live in, there are some exceptions for emission testing.

Vintage cars

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​Have a classic car? The answer to "what is an emissions test?" may be a little different for you.

Because most people aren't driving their classic cars daily, many states offer exemptions to emissions testing. Pennsylvania, for example, does not require emissions testing on any vehicle that has an antique license plate.

Driving off into the Sunset

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​Making sure to maintain your vehicle correctly will help a great deal with emissions testing. Whether you do the maintenance yourself or you employ a trustworthy mechanic is up to you.

If it is time to take your vehicle in for an emissions test, it might be a good idea to have your mechanic look your car over beforehand to make sure there is nothing he or she can see that would cause your vehicle to fail this test.

As stated previously, the answer to "what is an emissions test?" could be different in your state than it is in mine, so you must check your state regulations to make sure that you are following them correctly.

Leave us a comment below letting us know what an emissions test is in your state!


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