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 an Emissions Test

So what happens if your car fails an emissions 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 Smog Program

Nearly ten percent of all cars 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 may mean 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 being 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. Like 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 less 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. 

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. This can also be why you can’t pass the emission test. How to do smog testing in this case? 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 my 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 Us

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 a 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 the test mode, and suggest future repairs if needed. 

Don’t change the battery and the oil

The recently replaced battery may affect the results of the smog test. So, if possible, don’t change it before passing it 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.