5 Tips to Get Your Car to Pass a Smog Test

Call us now at (855) 547-1550
or email us at support@junkcarsus.com

Receive a guaranteed highest-priced quote for your junk car from the best junk car buyer by filling out the form online.

We’re open Mon-Fri: 8 am - 8 pm, Sat: 8 am - 3 pm
Edgar Moulton.


Edgar Moulton. Car Expert

Smog testing is something you have to do every two years. But many car owners neglect such inspections. They consider it frustrating, expensive, and time-consuming. In practice, it is relatively easy. If you have a car that has recently failed its smog test, read on to see why that may be and if it's possible to repair. If not, see what options you have for selling it legally and for the most money.

What Happens If Your Car Fails a Tailpipe Emission Test

Currently, 33 of the 50 states in the United States require a smog test. Among these 33 states, there are different levels of strictness regarding what it means to pass a smog test and what it means to fail one. Even among the same states, certain districts require smog tests while others don't. So, the answer to the question of how to pass a smog program directly depends on the state you are passing the test in.

So what happens if your car doesn't pass a smog test? If you take your car to an emissions test center and receive a failed smog test, you won't be able to register your car. Obviously, it's illegal to drive around without valid registration, so don't do that. Lucky for you, there are options for fixing whatever it is that is causing a smog test failure.

8 Reasons a Car Won't Pass a Smog Program

Every year, dozens of vehicles enter the list of the most hated car brands. There are many reasons why a car can be considered unreliable, and not passing a smog test is certainly one of them. Nearly ten percent of all vehicles that take a smog test will fail them, so if you're part of that ten percent, you're not alone. There are a few common causes that will result in a smog check failure. Let's have a look at them.

A damaged oxygen sensor

A gasoline combustion engine works by combining oxygen and fuel to create an explosion within the cylinder. When the oxygen sensor is faulty or failing, it won't input the correct fuel-to-oxygen ratio. This most often causes the car to use more gasoline than is usually required. More gasoline being used means greater emissions, which can lead to a car that's not passing smog.

A failed evaporative emission control system

The evaporative emission control system (more commonly referred to as EVAP) works in tandem with the fuel tank. Its purpose is to absorb gasoline vapors that evaporate from the gasoline in the fuel tank. When the EVAP doesn't do its job correctly, gasoline vapors are released into the atmosphere. If you've ever seen the mirage-like waves coming up from your fuel tank when you fill it with gasoline, that's what is constantly happening when your EVAP doesn't do its job.

Improper fuel mixture

As we said in point number 1, your engine requires the correct ratio of fuel and air entering the cylinders at all times to run efficiently. Sometimes, a car can run too "rich," meaning there is more fuel entering than required for the amount of air entering. When this happens, your vehicle will use more fuel than needed, and the smog check will notice this, resulting in a car that can't pass emissions. This can happen from any number of things, ranging from your fuel injectors being in bad condition to a clogged air filter.

Faulty ignition system

The ignition system in your car is combined with numerous parts and can be somewhat complicated. From improper ignition timing to defective components — if your ignition system is why your car won't pass a smog program, it may be costly to repair.

Defective catalytic converter

The catalytic converter (more commonly referred to as CAT) takes any leftover fuel and air not properly burned during the combustion process within the cylinder and burns it off more thoroughly so that the engine thoroughly burns off any fuel and emits fewer harmful emissions from your exhaust. The only way to test if this is what is causing your failed smog test is an expensive diagnostic tool called an exhaust gas analyzer (it detects carbon monoxide, among other gasses).

Those are the top 5 reasons why your car may have failed its smog test. However, there are simpler but less obvious reasons for failing the automobile emissions test. For instance:

Cold engine

To reduce the risk of failure in the smog test, let your engine work for at least 20 minutes before testing. During the cold period, the car may need up to 40 minutes to heat the engine.

Recent battery replacement

Failed smog test due to a new battery is yet another reason. You might be wondering how to pass smog after replacing the battery. The solution is also simple — you have to go on a car for 100–200 miles so that it "gets used" to the new battery and begins generating the correct data that will be checked during the test.

Recent oil change

The drivers report that dirty oil is the top reason why their car won't pass a smog test. What's more, it significantly harms the engine, so it is always better to buy the oil in trusted places and don't change it after you have found the option that suits your car. How do you pass a smog test in this case? Just get back to the oil you have previously used.

How to Get Your Car to Pass a Smog Test: 5 tips from JunkCarsUs

Below are some tips to make your car pass it.

Make sure your car is in technical order

One of the reasons for failing a test is that a car's engine needs complete repair. In this case, it is better to repair it and only then apply for a smog test. As one more advanced tip, consider applying for a pre-inspection service. The experts will help you identify the problems, check your car in test mode, and suggest future repairs if needed.

Don't change the battery and the oil

It is possible that your smog check failed due to a new battery, so don't change it before passing, since the engine should get used to a new battery in order to send the right signals and generate the right data necessary for passing an emission test. As for the oil, make sure to use the clean option two weeks before the test since the sediments can impact how the engine works.

Find a company that offers to retest your car

In addition to testing your car in advance, that is, using the smog pre-testing services, you can also find a company to retest your car. After repairing some malfunctions affecting the smog test success, you can retest it again to get a better result. Also, check the legislation of your state — some of them give the driver enough time to deal with technical troubles and reapply for the test.

Check the tires and inflate them

Tire inflation is also important for the emission check. When they are uninflated, the car can't run at high speed. The engine also can't consume the oil in the right way, leading to test failure.

Consider using a fuel additive

This is a controversial piece of advice. However, it can be a game-changer for older cars. Fuel additives are special substances that make the oil clearer, helping you pass an emission test. Make sure to choose the one of a high-quality, plus fuel the car with high-quality oil as well.

But what happens if you can't pass the smog test?

First, if your car didn't pass a smog test, it's not the end of the world. Strangely enough, it may even be a blessing in disguise. If your car got a "smog check failed" certificate, it means your car isn't running as optimally as it should be.

As you can see in our cash for clunkers program article, one of the main goals of the federal government regulating emissions is to reduce the overall carbon footprint of the automotive industry. This means if your car didn't pass, it's using more fuel than it is supposed to be. When your car uses more fuel, it's not only bad for the environment, but it's also bad for your wallet. So completing the necessary service and repairs to your vehicle might actually save you money in the long run. Of course, the best advice is to get regular inspections and complete the regularly scheduled maintenance.

So your car failed a smog check. Now what? Luckily, when your car fails a smog test, it will come with a report on why it failed the smog test. This will usually give enough of a clue to a skilled technician as to what's wrong with it, making it easier for him to fix it. So if you're wondering how to pass a smog check, it depends on what is wrong with your car.

In some states, like California, the repairs to your car must be done by a designated smog check technician. It may happen that your car won't pass smog in California the first time, then the repairs are completed, you must take it to a STAR facility. This is a smog check station that is designated by the state, not just a privately-owned auto mechanic shop. So if you're wondering how to pass a smog test after it failed the first time, the simple answer is to get the necessary repairs, then have it tested again.

Who Needs a Smog Check in The State of California

In the state of California, the California Bureau of Automotive Repair (BAR) and the California Department of Motor Vehicles (DMV) administrate the smog program.

Cars that were manufactured in 1976 and later are to go through the biennial (every other year) smog check program. Now, let's see for which vehicles the test is not mandatory. The test is not required for:

  • Eight model–years old vehicles*
  • Diesel heavyweight cars
  • Alternative-fuel vehicles (electric cars)

As for 1975 and older vehicles, owners must prove that the emission system is intact and a smog test is not required.

This exception is made with the consideration that all listed cars will pay a smog abatement fee for the first eight years before passing a smog check.

Please, note that the exception is only for in-state cars that were registered in California. Also, diesel cars of 1998 or newer models, lightweight cars, or specially constructed 1976 vehicles fall under this category too.

California counties in which smog inspection is required:

1. Alameda 2. Butte 3. Colusa
4. Contra Costa 5. Fresno 6. Glenn
7. Kern 8. Kings 9. Los Angeles
10. Madera 11. Marin 12. Merced
13. Monterey 14. Napa 15. Nevada
16. Orange 17. Sacramento 18. San Benito
19. San Francisco 20. San Joaquin 21. San Luis Obispo
22. San Mateo 23. Santa Barbara 24. Santa Clara
25. Santa Cruz 26. Shasta 27. Solano
28. Stanislaus 29. Sutter 30. Tehama
31. Tulare 32. Ventura 33. Yolo
34. Yuba

Primary rural counties are exempt from smog inspection.

Can You Sell a Car That Won't Pass a Smog Test?

If your car failed its smog test, and you don't want to splash out on the repairs, your next question might be, "My car didn't pass smog in California, can I sell it?" The answer is negative when your car won't pass the smog California program within 90 days before the sale date. It will be illegal. Please, bear in mind that what you do if a car does not pass a smog varies in different states.

But in fact, the decision to sell a junk car to avoid damage to the environment is the most ethical tactic you can choose in this case.

In other states, even if they require a smog test to get a valid registration, you can sell it without a passed smog test — but you may need written permission from your department of motor vehicles. When you make a car sale without a valid smog test, you will need to have both parties sign an agreement informing the buyer that the car is sold "as is," and there are no guarantees that it will pass a smog test.

So, now you know what to do if your car doesn't pass smog and also have an option for selling that car, but it may be a complicated process — and it's only legal in certain states. If you have a car whose engine won’t pass a smog test, and you’re unable to sell it due to legal reasons or because you can’t find a buyer who will buy it without a valid smog test, you have one last option, because it is legal to sell your car for scrap. You can use a scrap car value calculator to get an idea of its actual worth.

JunkCarsUs is the leading junk car buyer, and the answer to your question, "What can I do if my car won't pass the smog test in California?" Instead of making you donate a car because of the emission test failure, we can give you a top dollar instant offer for your car no matter how unsalvageable or totaled the condition it's in, no matter the state you're in, no matter the title it has, or if it has a failed smog check. We offer free towing, the highest price guarantee, and we even do all the paperwork for you! Our three-step process is the easiest and most hassle-free way of getting rid of your junk car. So if you're all out of options on what to do with your failed smog junk car, give JunkCarsUs a call at (855) 547-1550 and see how much cash you can get today.


What happens if I fail a smog test?

In the state of California, a smog check is required by BAR and DMV for vehicle registration. If your car can't pass smog in California or if you fail to do it every two years, your legal rights to drive a car will be terminated, as you won't get a car's registration. In such a situation, you can fix the problem and apply for a retest.

What can I do if my car won't pass a smog test in California?

If the car does not pass the smog inspection, contact the Bureau of Automotive Repair (BAR) Referee Program. They will help you find a solution. Or you can just do the necessary repairs, get rid of possible problems, and undergo a smog retest.

How long does it take to pass a smog check?

A smog inspection does not take long and lasts around 20 to 30 minutes.

How do you pass a smog test legally?

The only way to pass a smog test legally is to carefully check your car before the testing, eliminate all the malfunctions that can affect the result, and calm down. Even in the case of failure, you still have backup strategies to resolve the situation.

Can you sell a car that won't pass smog?

According to the general rule, you can't sell it. But there is still an option of selling a car with mechanical problems or failed a smog test to some companies, for example, JunkCarsUs.

Edgar Moulton.


Edgar Moulton. Car Expert

Rate this article:

4.93 out of 5 based on 11 votes

Write us

Contact Us

Feel free to contact us for any business, media, or personal inquiries:

Book Online

Please, submit your quote request form and we will get back to you in a minutes with our guaranted cash offer!

Enter your phone number *
Enter your email
City *
Zip code
Condition Of The Vehicle

We never share your information or spam you with our own emails or promos!