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What To Do If Car Doesn’t Pass Smog – Complete Guide

Smog tests are an essential part of owning a car. They ensure that your vehicle doesn’t produce harmful pollutants that can damage the environment and affect your health. However, if your car fails the smog test, it can be a significant inconvenience. Not only do you have to spend money on repairs, but you may also face penalties and fines. In this article, we will discuss what you can do if your car doesn’t pass smog.

Understanding The Causes Of Smog

Before we dive into the steps you can take to fix your car, it’s essential to understand what causes smog. Smog is a combination of various pollutants, including nitrogen oxides, carbon monoxide, and volatile organic compounds. These pollutants are typically produced by cars, trucks, and buses. When they react with sunlight, they create ground-level ozone, which is the primary component of smog.

Reasons Why Your Car May Fail The Smog Test

Several factors can cause your car to fail the smog test. Here are some of the most common reasons:

Malfunctioning Oxygen Sensor

The oxygen sensor is responsible for monitoring the amount of oxygen in your car’s exhaust system. If it’s faulty, it can cause your car to produce higher emissions, leading to a failed smog test.

Bad Catalytic Converter

The catalytic converter is a critical component of your car’s exhaust system. It converts harmful pollutants into less harmful ones before they are released into the atmosphere. If it’s not working correctly, your car can produce more emissions than allowed, causing it to fail the smog test.

Worn Out Spark Plugs

Spark plugs ignite the fuel and air mixture in your car’s engine. If they’re worn out, your car can’t burn fuel efficiently, leading to increased emissions and a failed smog test.

Dirty Air Filter

A dirty air filter can reduce airflow to the engine, making it work harder to produce power. This can cause your car to produce more emissions, leading to a failed smog test.

Leaking Exhaust System

If your car’s exhaust system is leaking, it can allow harmful pollutants to escape into the atmosphere, causing it to fail the smog test.

Steps To Take If Your Car Doesn’t Pass Smog

If your car doesn’t pass the smog test, don’t panic. There are several steps you can take to fix the problem. Here’s what you should do:

Check The Error Code

When your car fails the smog test, you’ll receive an error code. This code will tell you what caused your car to fail. You can use this code to diagnose the problem and figure out what needs to be fixed.

Fix The Problem

Once you’ve identified the problem, you can take steps to fix it. Depending on the issue, you may need to replace parts or fix leaks. It’s essential to fix the problem as soon as possible to avoid further damage to your car and additional fines.

Retest Your Car

After you’ve fixed the problem, you’ll need to retest your car. Make sure to drive your car for at least 20 minutes before the test to ensure that it’s warmed up and ready to go. If your car passes the test, you’re good to go. If it fails again, you may need to take more drastic measures.

Seek Professional Help

If you’re not sure what’s causing your car to fail the smog test, or you’re not comfortable fixing it yourself, seek professional help. A mechanic can diagnose the problem and fix it for you, ensuring that your car passes the smog test.


Failing the smog test can be stressful, but there’s no need to panic. By understanding the causes of smog and the reasons why your car may fail the test, you can take steps to fix the problem and ensure that your car passes. Remember to seek professional help if you’re not comfortable fixing the problem yourself.


  1. How often do I need to have my car smog tested?

Most states require cars to undergo smog testing every two years.

  1. How much does a smog test cost?

The cost of a smog test varies depending on the location and the type of car. On average, it can cost between $30 and $100.

  1. Can I still drive my car if it fails the smog test?

It depends on the state you live in. Some states allow you to drive your car for a limited amount of time after it fails the smog test, while others require you to fix the problem before you can drive it again.

  1. What happens if I don’t fix my car after it fails the smog test?

If you don’t fix your car after it fails the smog test, you may face fines and penalties, and you won’t be able to renew your car’s registration.

  1. How can I reduce emissions from my car?

You can reduce emissions from your car by keeping it well-maintained, using public transportation, carpooling, or driving a more fuel-efficient vehicle.

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