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What Is Emissions Testing: The Complete Guide


More attention than ever is being paid to environmental issues these days, and in particular, vehicle-based pollution. It’s not surprising, therefore, that government regulators go to great lengths to ensure that vehicles driven on the road are compliant. If unchecked, a typical car or truck engine can produce a variety of toxic emissions, and these can be harmful to not just the environment but to individual health and well-being. Consequently, many jurisdictions have introduced emissions testing to ensure that vehicles are compliant, and it pays to know what is involved.

What Is Emissions Testing?

In the United States, the Environmental Protection Agency (EPA) manages “clean” automotive technology and community programs that help to cut down on pollution. Vehicles are tested to determine if they meet certain emission standards and to ensure they comply with figures achieved by the EPA in their National Vehicle and Fuel Emissions Laboratory.

However, each state can set its own requirements for emissions testing, and some states are far more stringent than others. California is generally accepted to have the strictest regime of all, and the standards created by Californian state regulators are often adopted by others.

Why Is Emissions Testing Important?

smog from emissions

This is Beijing, home to over 21.5 million people, and the capital of China. It’s not the largest city in China, with that honor going to Guangzhou at over 44 million, but it’s one of the most polluted cities per capita in the entire world.

It’s so bad that a 2018 study named Beijing the 3rd most polluted city in the world, ahead of Guangzhou at 6, and Los Angeles at 10.

To give those numbers some context, over 1.8 million people die in China each year from pollution – which is nearly 4 times as many as are killed by smoking, the leading cause of preventable death in the United States.

Now, what you’re seeing in the photo above is an example of the toxic clouds of smog that sometimes blanket Beijing during the winter months. That sooty looking air is choked with industrial chemicals from two sources: coal fired power plants and cars.

This toxic soup degrades the lungs and contributes to a number of cancers and other diseases which kill the residents en masse.

Sometimes it can get so severe that schools and factories close, flights are canceled, and life grinds to a halt. At one point prior to the 2008 Olympics, the smog was so bad that Chinese government had to shut down factories and stop car usage.

Does this seem incredibly grim?

It should.

While getting your emissions tested might seem trivial to you, by taking the time to get your car tested, you’re playing a part in ensuring that you don’t contribute to the worldwide pollution problem we have.

An emissions test helps ensure your vehicle is properly processing toxic emissions before emitting them into the atmosphere.

In other words, it’s important. Don’t take it lightly!

What happens during an emissions test?

emissions testing setup

If you have a vehicle that’s newer than 1996, all an emissions test consists of is a quick trip to the mechanic.

Your mechanic will hook your car up to what’s known as an OBD reader, which can check the engine, transmission, and emissions control systems and then let the operator know if there are any issues with the car.

Your mechanic will then perform a visual inspection of your car to ensure that everything appears to be in good working order. 

Tricks For How to Pass An Emissions Test

tricks to pass an emissions test

Of course, you’ll always want to pass your emissions test. The good news is, with regular maintenance, you won’t have anything to worry about.

However, if you’re looking for a checklist of things to go over prior to your inspection, we’ve got you covered.

Change your oil and oil filter: Having clean oil and a new oil filter will go a long way. Change both before the inspection. If your oil is dirty, the PCV system can absorb some of the vapors from your dirty oil. When these dirty vapors burn, they read as emissions on your test which is no good for you.

Plus, burning dirty oil pollutes the environment. You don’t want that.

Change your air filter: Depending on your driving conditions, you should replace your air filter every 15,000 – 30,000 miles anyway, but if you’re about to get an emissions test, double check it. With a blocked air filter, not enough air will get into your engine, which will cause it to run hotter, which will heat the exhaust up and put out more pollutants, which can cause you to fail the test.

Change your spark plugs: Older spark plugs can cause your car to misfire, which releases pollutants. Having working spark plugs can also keep your car from experiencing a catalytic converter failure – which is not only expensive – but will cause you to fail the emissions test.

Just one misfire can dump enough unburned fuel into the exhaust which can overheat it and damage the converter.

Check your coolant:  Low coolant can cause your engine to draw in more air – which will cause it to run hotter and output more pollution. You should also check the color of your coolant, which is something we’ve talked about in our article on common repair mistakes.

Check your cooling fan: Turn on your air conditioning and then check the engine to make sure the fan is spinning. If it isn’t, your engine could overheat and put out more pollutants. During the actual test, your car isn’t going to be moving and sucking in air like it would be while driving.

Mind you, this is only really applicable if your car is older than a 1996! Otherwise, just do the above.

I think you can see why having a working cooling fan is pretty important!

Passing An Emissions Test With A Check Engine Light On

emissions check enging light

All cars made after 1996 are plugged into a computer to check emissions. However, if you have a check engine light on, you’re going to automatically fail the test.

There are thousands of possible codes for a check engine light and we can’t cover all of them here. While a check engine light is serious, and you should always address it as soon as possible, there is a way to quickly clear the check engine light prior to inspection if you need to pass in a pinch.

You’ll need an OBD-II code reader, and some time to drive around prior to the inspection. The good news is, an OBD-II code reader can be had for less than $20 dollars on Amazon.

If you don’t have $20 dollars, you can stop by a mechanic and ask them to reset the light as well, which they may do for free.

What you’ll need to do is plug the OBD-II reader into the vehicle’s port, which in most cars is located under the driver’s side dashboard, usually towards the driver’s side door.

Once it’s plugged in, take a look at what codes are causing the check engine light and then go ahead and reset them using your OBD-II reader. This will clear your check engine light, but you’re not done yet.

Drive around for at least half an hour prior to the test. A full hour would be even better. A mix of city and highway driving will give you the best results. The way we recommend doing it is driving about 15 minutes at city speeds (between 30-45 MPH) followed by 15 minutes at highway speeds (55-70 MPH). Make sure to fully stop the car and do some gentle acceleration during the city piece, and you’ll be in good shape. 

Do this correctly and you should pass the test. Just make sure that you get whatever is causing the check engine light fixed as soon as possible. You don’t want to have to pay for costly repairs!

What Do They Check For On An Emissions Test?

checking emissions test

By now it’s probably no surprise to you, but your car can release dozens of toxic gases which reduce air quality and increase pollution.

When you take your car in for an emissions test, it’ll be tested for the following:


  • Nitrogen Oxide (NOx)
  • Carbon Monoxide (CO)
  • Particulate Matter (PM)
  • Non-Methane Organic Gases (NMOG)
  • Formaldehyde (HCHO)

The vehicle emissions test procedure is simple. By plugging in an OBD-II reader, the technician will check that your emissions control systems are working correctly.

What Happens If Your Car Fails An Emissions Test? What If You Fail It Twice?

If you’re in a state where you’re required to have your car tested for emissions, failing an emissions test means that the DMV won’t re-register your vehicle.

If your registration is current, you’ll be temporarily okay. If it isn’t, then you need to quickly get your car fixed.

The good news is you should get a report if your car fails on what you need to fix.

Most states will give you around 60 days to fix your vehicle and then have the emission re-tested.

If you fail a second time, depending on where you’re located, your vehicle may qualify for a cost waiver, where you’ll be able to have the repairs done in a certified shop in your state.

To qualify for one of these waivers, you’ll need to meet certain conditions which may include:

  • Economic: You’ll need to have spent a certain amount on getting your vehicle tested and repaired.
  • Visual: Your car will need to pass a visual inspection of it’s emissions control equipment
  • Retest failure after repair: If you get the recommended repairs after failing the first time, and then your car fails a second time.

This will vary depending on the state you’re in. We recommend looking up your individual state’s emission control procedures, as there are almost always options to get your car back into compliance. 3

What Parts Are Tested as Part of an Emissions Test?

When the vehicle is subject to a manual check, certain simulations are performed to check if dangerous gases like carbon dioxide are being allowed to reach the atmosphere. Gas analyzing equipment is connected to the tailpipe on the vehicle, and this is set this up to monitor the four main gases laid down in EPA emission standards.

Usually, the gas analyzer will be inserted into the tailpipe to measure and check for levels of oxygen, carbon dioxide, hydrocarbons, and carbon monoxide, while some states will check for nitrogen oxide as well.

What Causes a Car to Fail an Emissions Test?

failing an emissions test

Before you take your car in for an emissions test you should be aware of the most common reasons for failure, and ideally, make sure that you have checked (and potentially addressed) these issues.

List of failures that should be taken care of prior to taking your test.

  1. If your air-to-fuel mixture is too rich, then you may have clogged injectors or a bad oxygen sensor. If the vehicle is running too rich, then fuel can find its way through into the exhaust and cause the catalytic converter to fail as well.
  2. If the catalytic converter is faulty, then it will be unable to convert those toxic gases and render them safe for release.
  3. Cars that have an evaporative emissions control system fitted may fail if it is not functioning as it should. This system is designed to stop gasoline vapors from leaking out of the fuel tank and finding their way into the atmosphere. Most of the time, failure here is down to cracks in the hose or blocked vents.
  4. It’s also important to check the integrity of the gas cap, as although this is one of the biggest causes of failure, it’s one of the simplest to fix. It is often a good idea to replace a standard gas cap with one that is specifically designed to help ensure you pass the emissions test.
  5. Spark plugs should be changed on a regular basis to keep the car running as efficiently as possible. If they’re not, they can affect the combustion process and lead to an increase in emissions.
  6. If your air filter has not been changed or cleaned for some time, this could lead to a higher level of hydrocarbons in the test reading.
  7. You may also find that the oil in your engine can release hydrocarbons if it has been left to circulate for too long and is in generally poor condition.
  8. Inspectors will often fail a car simply because the check engine light is illuminated. This light could come on for any number of reasons, and this may have nothing to do with the vehicle emissions. Consequently, it’s important to ensure that the light is working correctly before presenting the vehicle.

How Much Do Emissions Repairs Cost?

It’s hard to say how much your emissions repair will cost, but to make it a little easier, here are a few common problems that’ll cause you to fail an emissions test and how much they cost to fix.


Malfunctioning Part

Cost To Repair

Rich Air-Fuel Mixture

Fuel Injectors


Rich Air-Fuel Mixture

O2 Sensor


Worn Spark Plugs

Spark Plugs


Emissions Control System Defect

EVAP System


Leaking Gas Cap

Gas Cap


Check Engine Light

Many Possible Repairs


Dirty Air Filter

Air Filter


Damaged Catalytic Converter

Catalytic Converter


The good news is, most of these repairs are inexpensive – and catalytic converter failure is uncommon. If you’re covered by a Protect My Car warranty, even a catalytic converter failure is no big deal. We pay for those.             

How Long Does An Emissions Test Take?

emissions testing time

Emissions tests are quick. If your vehicle is 1997 or newer, the visual inspection and OBD-II reader check can be done in about 15 minutes.

Older vehicles will take a little bit longer, owing to the additional time needed to hook your car’s exhaust into the testing system. From experience, these can take up to 30 minutes depending on which shop you go to.

Generally, you’ll get quicker results from your dealer or any shop that specializes in emissions testing, if you’re trying to squeeze an emissions test in at lunch, for example.

What Happens If You Don’t Get An Emissions Test?

emissions no test results

As previously mentioned, if your car falls out of compliance with emissions testing, you won’t be able to renew your registration at the DMV.

Driving with an expired registration (at least in Florida, where we’re located) is classified as a second-degree misdemeanor punishable by up to 60 days in jail if your registration has been expired for more than 6 months.

Chances are you probably won’t end up in the clink, but you’ll likely end up with a hefty ticket, which can start at around $200-$300 dollars. 

How Do US Emission Standards Differ From Europe?

How does the United States compare to other continents like Europe, given that airborne pollution is felt to be contributory to the global problem?

It’s difficult to compare emissions standards across different countries, but even though standards brought forward under the Obama administration were quite strict, they were still less onerous than those laid down by the European Union. Even so, there are differences in what each region focuses on. For example, the US is very strict on nitrogen oxide and particulate matter, while the EU focuses more on carbon monoxide and carbon dioxide.

What Is an Emissions Test Cycle?

emissions testAn emissions test cycle is a procedure that makes it possible for exhaust emissions to be accurately determined for individual engines and vehicles. The cycle will lay down the conditions for vehicle or engine operation during a given test based on speed, engine load, and operating temperature. 

Results are both realistic and accurate and represent “real-world” conditions that the vehicle or engine may be subject to during normal use. Original equipment manufacturers can use these readings to program the engine management systems on all their vehicles, with the goal being to keep emission levels below those standards.

What States Test Emissions?

states that emissions testEven though the EPA has had emissions testing regulation for some years now, not all states are required to comply, and while most do stipulate some type of emissions testing, this can vary within state boundaries and can affect how often the individual vehicle is assessed.

For example, many states determine that emissions testing is more important in areas that have high traffic levels or that constitute a major population center. As it can be difficult to know where a test may or may not be required, consumers should always refer to government websites or information provided by the individual state in question.

What Are State-By-State Emissions Requirements?

The following states only require emissions testing in specific cities:

  • Arizona ⁠— Phoenix and Tucson areas.
  • Colorado ⁠— Denver and Boulder areas.
  • Georgia ⁠— All the Atlanta metro counties.
  • Idaho ⁠— Boise and Ada County.
  • Illinois ⁠— Chicago and East St Louis.
  • Indiana ⁠— Gary metropolitan area.
  • Maine ⁠— Cumberland County and the Portland area.
  • Maryland ⁠— Baltimore and Washington DC metro.
  • Missouri ⁠— Jefferson and Franklin counties.
  • Nevada ⁠— Las Vegas and Reno.
  • New Mexico ⁠— Albuquerque.
  • North Carolina ⁠— 48 separate counties.
  • Ohio ⁠— Cleveland and Akron.
  • Oregon ⁠— Portland and Medford.
  • Pennsylvania ⁠— Philadelphia and Pittsburgh areas.
  • Tennessee ⁠— Memphis and Nashville.
  • Texas ⁠— El Paso, Dallas Fort Worth, Houston, and Austin.
  • Utah ⁠— Salt Lake City, Provo, and Ogden.
  • Virginia ⁠— Arlington and DC.
  • Washington ⁠— Vancouver, Tacoma, Spokane, and Seattle.
  • Wisconsin ⁠— Milwaukee and southeast Wisconsin.

Meanwhile, the following states require testing in all areas:

  • California (except for a few ZIP codes).
  • New Hampshire.
  • New Jersey.
  • New York.
  • Vermont (for vehicles that were manufactured after 1996).
  • Washington DC.

The states not mentioned do not require emissions testing.

California Leads the Way

California Emissions TestingCalifornia is the “gold standard” for emissions testing in the US. Within the state, emissions tests (also known as smog inspections) are needed for all vehicles except motorcycles or vehicles made before 1976 and diesel-powered vehicles made before 1996 that have a G.V.W. over 8,500 pounds. Owners that live in areas that have a biennial smog certification program must have an emissions certificate when they present a vehicle for renewal.

Rules are complicated, but in general:

  • Vehicles that are less than eight years old are exempt from the biennial requirements in terms of registration renewal. 
  • When a vehicle is sold, smog certification is required unless the transfer is between certain members of the family.
  • Once a smog certification has been issued, then it is good for 90 days from that point, and registration renewal will need to take place within that period.
  • While emissions inspection is required in most counties, certain counties limit smog certification to specific ZIP codes only.

Section 177 States

As part of its Clean Air Act, California has the most stringent policies in the nation when it comes to reducing carbon emissions from road-going vehicles. In fact, it has a federal waiver that allows it to implement even stricter emission standards than those laid down by the EPA.

All this information is laid down in a statute known as Section 177, and other states have been so impressed by this legislation that they have adopted it themselves. Known as the Section 177 states, these are Connecticut, Delaware, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, and Washington. At one time, Arizona joined these states, but that legislation has been subsequently repealed.

Such has been the impact of Section 177, that car manufacturers need to refer to both the EPA guidelines and the Section 177 rules when planning their emissions compliance.

What Do I Need to Bring to an Emissions Test?

If you are required to pass an emissions test, then you will have to take certain documentation with you when you present for the inspection. For example, in California, you will need to take in proof of vehicle registration as well as a form of payment. The price will vary according to the licensed station, and you should shop around to find the best deal.

California Smog Exemption Form

in California, some drivers are eligible to register a vehicle without having a smog certificate. This program is administered by the state of California for those who are income-eligible, and if they are, they can receive a two-year extension to complete any repairs necessary that are related to vehicle emissions.

Compliance and Peace of Mind

extended car warranty

Although emissions testing is not mandatory in all 50 states, it’s nevertheless a good idea to ensure that your vehicle is in good condition and that all fitted parts are working correctly.

This will include components that were fitted by the original equipment manufacturer, including important components like the oxygen sensor and the catalytic converter. This approach is recommended for every car owner, especially if you want your vehicle to last as long as possible.

Now here’s the truth: most emissions repairs are inexpensive and won’t be covered by an extended warranty. Considering that you can get a state level waiver for the repair costs anyway, you’re probably better off doing so.

But what happens if your catalytic converter is damaged?

Well, for one, you’ll be staring down the face of an extremely expensive repair, that will run into the thousands of dollars.

If you’re worried that this is going to happen, an extended warranty from Protect My Car can really give you that peace of mind.

We’ll cover the expensive repairs to emissions parts including your catalytic converter. It’ll also cover you in the case of the dreaded check engine light.

So don’t stress.

Pass your emissions test, and make sure you have extended warranty coverage from us to keep your car as green as you can.

Get a free quote with us today and see how much you can save on your auto repairs.


About Protect My Car

Protect My Car is a vehicle service contract provider, also referred to as extended car warranty provider, with multiple coverage plans for new and used vehicles with low to higher mileage to help meet your needs and budget. Protect My Car customers work directly with the company for customer service, claims administration and contract financing. No middleman or the need for third-party approval. All Protect My Car Plans include best-in-class claims and customer support, 24/7 roadside assistance, free oil changes and tire rotations and the exclusive PMC Rewards Plan, providing daily deals, giveaways, coupons, and thousands of ways to save money every day. Protect My Car has a 30-day money-back guarantee.

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