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How to Pass Emissions Test (10 Tips)

If you’re wondering how to pass an emissions test, then you’ve come to the right place. We have all the specific techniques you need to ensure that your vehicle passes the test with flying colors. Over millions of drivers in America alone complete their emissions tests every year, so it’s crucial to make sure that you’re prepared to do yours correctly.

By following our comprehensive guide on how to pass emissions test, you can save yourself time and hassle when navigating this often-confusing process. Read on to learn everything you need to know before you head out for your emissions test.

1. Get the “Check Engine” light to turn off

If you want to pass your emissions test with flying colors, the first thing you need to do is make sure that the dreaded “Check Engine” light is not illuminated. This warning light indicates that there is something wrong with your vehicle, and that’s not good news if you’re trying to pass a smog test.

One possible culprit for this light coming on is a faulty oxygen sensor, which plays a vital role in gauging your emissions output. Fortunately, cleaning or changing this sensor is relatively easy and affordable, so it’s definitely worth doing before you schedule your test.

2. Take your car for a spin on the highway

One simple trick to get your car all cleaned up and ready to go is to take it for a spin on the highway. It’s like a spa day for your catalytic converter! You see, the catalytic converter can get clogged and needs to be cleaned out.

By driving your car at high speeds, the converter heats up and helps to clear out any build-up. Just remember to do this a few weeks before your test so everything is nice and clean when you head to the testing center.

3. Fill up the engine with oil

If you want to pass your emissions test, one great tip is to refill your engine oil before heading out. Your engine’s performance can drastically improve when you’ve got fresh oil running through it. If you’ve been putting it off for a while, it might be worth moving your test date a little further down the road just so you can give your car the TLC it needs. With clean oil, your vehicle will run smoothly, efficiently, and release fewer pollutants into the air.

Related: Overdue Oil Change Symptoms

4. Tune Your Vehicle Before the Test

Did you know that the number of harmful emissions coming out of your car is directly related to how it’s tuned? If your car is running on a rich air-fuel mixture, it’s going to emit more pollutants and you’re more likely to fail the test. That’s why it’s important to re-tune your car to run on a lean air-fuel mixture before the test.

Don’t worry, you can always switch it back to your preferred setting once you pass.

5. Ensure your tires are correctly inflated

Low tire pressure can not only affect your car’s fuel efficiency, but it can also cause your engine to work harder than it needs to. This extra work can lead to a rise in the production of harmful gases, which is exactly what you don’t want during your emissions test.

So, before you head to the testing facility, take a few minutes to check your tire pressure and make any necessary adjustments. It could make all the difference in ensuring that your car passes with ease.

Related: Why Is My Tire Pressure Light Blinking?

6. Ensure all the monitors have run

Make sure all of your car’s monitors have run successfully before heading to the testing center. These self-tests run by your car’s computer are essential for ensuring your emissions are within legal limits. If a monitor has not run, your car will be given a “not ready” result, which means you’ll need to take extra steps before you can pass.

7. Check the Fluid levels

The dynamo testing method used during the test involves pushing your car to high speeds, which can put a significant strain on your vehicle’s engine. A lack of sufficient fluids, such as oil or coolant, can increase the risk of damaging your engine, resulting in costly repairs. By checking your fluids beforehand, you can avoid this risk and have peace of mind when taking your car in for its emissions test.

8. Clean the Engine System

Before you head in for your test, consider using a premium fuel system cleaner that features Polyether Amine – this powerful detergent can work wonders at removing carbon buildup from the engine, subsequently reducing the amount of emissions your vehicle gives off.

While it might take several uses of a lower quality cleaner to achieve the same effect, a top-quality option can do the trick in just one use.

9. Preventing Rust

No one likes to see rust on their car, but did you know it could affect your ability to pass an emissions test? That’s right, rust isn’t just an eyesore; it can actually compromise your vehicle’s structural integrity and pose a safety hazard.

During an emissions test, a technician will check for any rust and determine whether it’s a direct threat to your safety. If it is, you’ll need to address the problem before you can legally drive your vehicle.

10. Get a Mock Inspection

One of the options available in some states is a mock inspection. This type of test is designed to give you an idea of what the real test will be like, including any repairs and adjustments that may be required.

By getting a mock inspection, you can identify any issues or problems with your car ahead of time and address them accordingly. This can help you to avoid the stress and frustration of failing the actual test, and make sure your vehicle is in top shape for the road ahead!


What causes a car to fail emissions test

How-to-Pass-Emissions-Test (1)
How-to-Pass-Emissions-Test (1)

One of the most likely culprits for a failed test is a faulty oxygen sensor. This lil’ part can cause problems with your car’s check engine light, and it’s definitely not something you want to ignore. Thankfully, getting a replacement isn’t super hard – but it can be a bit pricey. You’ll likely be paying somewhere between $346 and $395 for the part itself, plus another $61 to $77 for labor costs.

While it’s not exactly a fun expense, it’s definitely worth it consider how important it is for your car to be in good working condition.

Additional Reasons for Emissions Test Failure:

Your car’s battery was disconnected recently:

If your battery has been out of commission in the last couple of weeks, your car’s OBD system may not have the necessary information stored for a proper inspection. Don’t fret, though! Simply give it some time to collect data again and return for a retest in about a week or so.

The data link connector is faulty:

One reason for such failure is the Data Link Connector (DLC) or the OBD2 port. This port is what connects your vehicle to the inspector’s testing system, and any issues with it, whether it’s a faulty port or a bad connection, can cause your test to come back unsuccessful. So, before you cruise into the testing center, it’s best to check your DLC to ensure it’s functioning well to avoid any unnecessary failures.

The “check engine” indicator light is on:

Don’t panic just yet! This could be a sign of exhaust system issues, but there are other culprits to consider as well. Faulty battery or cables could also trigger the alert, along with aftermarket alarm systems.

Actual test failure:

When you receive your inspection report and see those dreaded diagnostic trouble codes (DTCs) listed, it’s important to take the report to a qualified mechanic. Maybe it’s something as simple as replacing an oxygen sensor or cleaning the air filter.

Several factors can lead to an actual emissions test failure, including:

Exhaust system issues:

This system is responsible for redirecting burnt gases from the engine and filtering them out through the exhaust pipe. The catalytic converter is a crucial part of this process, as it turns some of the harmful gases into less harmful ones like water and carbon dioxide. If something goes wrong with the catalytic converter, your car may not meet emissions standards, resulting in a failed test

Other system issues:

Did you know that other system issues, besides your exhaust system, can lead to a failed test? That’s right! Your ignition system, fuel injection system, and air injection system all play a crucial role in reducing the number of pollutants that end up in your exhaust.

Unfortunately, there are multiple points of failure in each system that can quickly lead to a failed emissions test. So, if you’re experiencing any issues with your vehicle’s functionality, it’s always best to get it checked out sooner rather than later.


What happens if your car fails an emissions test?

When your car fails this test, it typically means there is an issue with your vehicle that is causing it to produce too many pollutants. Whether it’s a clogged air filter or a faulty oxygen sensor, you’ll need to take your car in to be serviced or repaired before you can pass the test and renew your registration. But don’t fret, you typically have a grace period where you can legally drive your car before retaking the emissions test.


What happens if you fail an emissions test twice?

Well, don’t worry too much. In many cases, you may be eligible for a waiver due to economic hardship or a maximum repair cost limit imposed by your state or local government. This means you can save some money and not stress too much if your car fails the test a couple of times. So, if you find yourself in this situation, be sure to do your research and see if you qualify for any waivers or assistance.


FAQs about How to Pass Emissions Test

How to pass emission test with engine light on?

To pass the emissions test, the light must be turned off. The best way to do this is to run a scan with a diagnostic tool to identify the problem, and then make the corresponding repair. It may seem like a hassle, but taking care of the issue now will save you time and money in the long run. Don’t stress, we’ve all been there – just take a deep breath and know that you’ve got this under control!

How many times can you fail an emissions test?

Depending on where you live, you might be granted a waiver or you might not be able to renew your registration. So, the best thing you can do is try your best to pass the test on the first try, but if you do fail, be sure to perform any necessary repairs before taking it again.

What is the best day to go to emissions testing?

Well, here’s a tip: weekdays from 4-5 p.m. and Saturday afternoons tend to be the fastest times to get your testing done. Not only that, mid-month is a good time to have your emissions tested as well. And to make things even easier, you can check for stations located conveniently near your home or work and even see live wait times to avoid any unnecessary waiting.

What states require testing?

Here is a table listing the states and areas that require emissions testing:

StateAreas Included
ArizonaPhoenix and Tucson
CaliforniaAll Areas
ColoradoDenver and Boulder
ConnecticutAll Areas
DelawareAll Areas
GeorgiaAll 13 Atlanta Metro Counties
IdahoCity of Boise and Ada County
IllinoisChicago and East St. Louis
IndianaGary Metro Area
MaineCumberland County, and the Portland Metro Area
MarylandAll DC Metro and the City of Baltimore
MassachusettsAll Areas
MissouriJefferson County and Franklin County
NevadaCities of Reno and Las Vegas
New HampshireAll Areas
New JerseyAll Areas
New MexicoAlbuquerque Metro Area
New YorkAll Areas
North Carolina48 Counties – see the NC DMV site for more info
OhioCities of Akron and Cleveland
OregonCities of Medford and Portland
PennsylvaniaCities of Pittsburgh and Philadelphia
TennesseeCities of Nashville and Memphis
TexasCities of Austin, Houston, Dallas/Fort Worth and El Paso
UtahCities of Ogden, Provo and Salt Lake
VermontAll Areas (1996 or newer vehicles only)
VirginiaAll DC Metro and Arlington
WashingtonCities of Seattle, Spokane, Tacoma and Vancouver
Washington DCAll Areas
WisconsinAll of SE Wisconsin and the City of Milwaukee



To pass an emissions test, regular vehicle maintenance is key. This includes changing the oil, checking coolant levels, and replacing worn spark plugs or oxygen sensors. Avoid fuel treatments with detergents or chemicals that can interfere with the oxygen sensor. Be sure to have your vehicle serviced at least six weeks before the emissions test.

With these simple tips, you’ll be well prepared to score well on your next test. Speak to your mechanic for additional guidance on how to pass emissions test. Remember: when it comes to passing emissions, preventative maintenance is your best friend!

Thank you for reading!

1 thought on “How to Pass Emissions Test (10 Tips)”

  1. Is it possible to pass an emissions test even if the check engine light is on? I’m wondering if turning it off will still allow me to pass, or if they can detect that it has been reset in any way.


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