How To Pass OBD II Emissions Test With Flying Colors

How To Pass OBD II Emissions Test With Flying Colors

Every year in the U.S., one passenger vehicle emits 4.6 metric tons of carbon dioxide.

Since there are more cars on the road than there were before, this has resulted in even more air pollution, which is why it’s important to get a vehicle emissions test. 

What is an emissions test? This is sometimes called a smog check and it helps to ensure that your car meets the emissions standards of the Environmental Protection Agency (EPA).

This is a test that should be done every two years. With that in mind, let’s explore what you should know about the emissions tests and how to ensure that your car passes them. 

Does Every State Require Emissions Tests?

Does Every State Require Emissions Tests?

If you reside in the United States, you might wonder if your car needs to have an emissions test. It probably does, because over 30 states in the U.S. require some type of emissions testing by law.

How comprehensive this test will be will depend on the rules in your state. For example, in New York, every car owner will have to ensure that their car undergoes an emissions test every year.

Cars that were made in 1996 or more recently will undergo an OBD 2 test, while in Colorado some gas and hybrid cars are exempt from emissions testing within the first seven years but cars older than 1981 must be tested annually.  

Types Of Emissions Tests


There are two types of emissions tests:

Tailpipe test

This is when an exhaust gas analyzer is inserted into the car’s tailpipe.

This device measures the levels of carbon monoxide and hydrocarbons, which are both air pollutants. It will also measure oxygen and carbon dioxide levels.

Onboard Diagnostics (OBD2)

The OBD2 test makes use of a scan tool that’s inserted into the car’s diagnostic port.

This communicates with the car’s onboard computer to ensure that there are no emission problems that are being displayed.

OBD is useful for emissions testing because it alerts you to any problems that are wasting fuel and shortening the car engine’s lifespan. Similarly, it can inform you if your car is contributing to unhealthy air because of its pollutants.

This type of test is only done on cars that were made in 1996 or later, though.

Note that a car emissions test will usually also include an inspection

How To Pass A Emission Test

To ensure that your vehicle passes these crucial tests, you should do the following, whether you’re having a tailpipe or OBD test.

How to pass a tailpipe test


Start by warming up the engine

You should drive around for about half an hour before the test because when your engine is warm, this will ensure that it’s at the right temperature for testing.

Get regular car maintenance

You should have your car serviced regularly, depending on when the manufacturer recommends that you do so.

This will ensure that tasks such as fluid changes and filter replacements are done promptly so that your car is in good condition.

The bonus of doing this, of course, is that you’ll prevent sudden, serious problems from occurring and costing you a lot of money.

Fix any other problems

You should make sure you repair any car problems, such as if your engine is stalling.

This is because engine problems can result in an increase in tailpipe emissions. You want to avoid those before the emissions test.

Similarly, you will need to ensure that your car is not displaying the “check engine” light as that signals it has a problem.

It’s best to check your car and let it undergo any necessary repairs before taking it for an emissions test. 

How to pass an OBD 2 emissions test

  • Ensure the “check engine” light is off. This is important to solve any problems with the car before you take your car for an OBD2 emissions test.
  • Check the monitors. Your car has an in-built computer that conducts self-tests which are known as monitors. During an emissions test, the technician will want to see that all of the monitors have successfully run. If you’ve recently reset these monitors, such as by disconnecting the battery or clearing diagnostic trouble codes from the computer’s memory, you will need to run the monitors. If you don’t, your car won’t be ready for the test. Use a scan tool to check that the monitors have been run.
  • Don’t take your car for an emissions test if you’ve changed its battery. Similarly, you shouldn’t go for a test if your car battery has died or was recently disconnected. This is because if the battery has less than five volts, the car’s computer memory will be lost so your car won’t be able to pass the emissions test. To ensure that its OBD2 system is working properly and has done all of its onboard tests, the car needs to be driven in varying conditions for up to seven days, then you can go ahead and book a test because you’re more likely to pass it.

What Can Cause Your Car To Fail An Emissions Test?

What Can Cause Your Car To Fail An Emissions Test?

There are various reasons why your car could fail its emissions test, so make sure your car has none of the following problems. 

  • Engine and transmission problems: Either of these car components can cause more tailpipe emissions to be produced, which will cause your car to fail the smog test.
  • Emission equipment that fails: Many cars have emissions equipment, such as exhaust fan recirculation systems and catalytic converters. If any of these have problems, your car could fail its smog test.
  • Air or fuel problems: As you know, your car’s engine requires a precise blend of fuel and air in order to work at its peak. If this blend is not accurate, it could cause problems – and result in your car not passing the emissions test.
  • Sensor problems: Modern cars contain many sensors, so any problems related to their data network or wiring can lead to problems with the emissions test.
  • Ignition system problems: Your car’s ignition system has components that ignite the air and fuel in the engine. If this fails, then it can lead to an engine misfire. Again, your car won’t pass an emissions test if it has this problem.

Your Car Failed An Emissions Test – What Now?

Your Car Failed An Emissions Test - What Now?

If you’re in the unfortunate situation of having failed your car emissions test, your car will have to be inspected.

You’ll receive a vehicle inspection report, repair shop card, certificate, as well as information pertaining to the vehicle repair.

A mechanic will be able to find out what the problem is that caused the vehicle to fail its emissions test and then repair it so that you can try the test again and pass it the second time around. 

Can’t You Just Switch Off Your “Check Engine” Light Before The Test? 

Can’t You Just Switch Off Your “Check Engine” Light Before The Test?

You might think you can just switch off your car’s “check engine” light before the test, but it won’t help you.

OBD2 systems store their codes and they won’t go away unless the vehicle’s computer runs its own tests. So, don’t try to turn off the light because it won’t help your car to pass the emissions test.

Even if you manage to do checks on your vehicle and turn off this light, the computer will rerun its test, which will merely put the light back on – and result in your vehicle failing its emissions test. 

Related Questions 

How often should your vehicle have an emissions test?


This will vary depending on your local government, which will also determine which car model year is either subject to or exempt from emissions testing.  

How long does an emissions test take?

You can expect an emissions test to take approximately 30 minutes, so it doesn’t take a long time.

How much does an emissions test cost?

Depending on the state in which you live, this test usually costs between $15 and $25. If your state requires you to do annual testing for your vehicle, the cost will usually be lower. 


Having a car emissions test is important to ensure that your vehicle is working properly. If it’s not, it could be contributing to the air pollution problem. 

However, there are things you need to know about these tests and how to pass them.

In this article, we’ve looked at how to pass OBD ii emissions test and what you need to know about them so that your car doesn’t fail because of some issue that could have been avoided.


Leave a Comment

Your email address will not be published. Required fields are marked *