Smog Test The When, Why, How Guide

More than likely one of the priorities regarding your vehicle is keeping it clean and looking its best. Taking care of its regular routine maintenance is also a very important aspect to consider. One thing that may come up and become routine is your annual smog test, also known as an E-check or emissions test, depending on the state you reside in.

A passing smog test is important because for many it is necessary in order to register and drive your vehicle legally. What exactly is a smog test? Why do you need to get one and what should you expect? This article will give you an overview of a basic smog test and give you helpful information to know.

What Is a Smog Test?

A smog test is done at an official testing center or a mechanic shop where they have been issued a license to legally inspect your vehicle under specific regulations. The test will check for issues in your exhaust system, including your catalytic converter. A properly functioning system will be free of leaks and will pass the test since it will be in compliance with set forth regulations. It is also meant to help prevent unnecessary environmental pollution. Another plus is that when your emissions system is working as it should, your engine will function at its peak and you will get better gas mileage as a result.

  • The smog test itself is governed by each state, meaning, every state will have its own ability to regulate how often, if at all, the smog test is required. There are seventeen states that currently require periodic testing which may be every year or every two years. Some will require a test on any vehicle brought into the state.
  • There are also specifics on the age and type of vehicle that will cause you to be able to get off without needing a smog test done, or requiring it to become part of your annual to do list.
  • Even though a clean air act is to thank for the arrival of smog testing, there are still states that were allowed to bypass the need for one. Therefore it is important to check with a local DMV to see what your state requires in regards to smog checks.

What to Expect at a Smog Test

When you bring your vehicle into a testing center, you will hand over your keys. A trained testing agent will pull your vehicle into a driving bay. Your vehicle will then be subject to a visual inspection and hooked up to a computer. The representative will then get into your vehicle and drive it to simulate different driving conditions. While this occurs, the computer will be recording the output levels to ensure there is no pollution present or any excessive exhaust.

Once the test is over, your vehicle will be drive out of the bay and your keys will be returned to you. You will pay a fee and receive a printout that states whether you passed or failed the smog test. If you pass, you are ready to go and complete your registration. If you fail, you are given a time limit to correct the issues found and return for a retest. You can also use the printout to give to a mechanic when you seek repairs.

General Specifications of a Failed Smog Test

1. Vacuum leaks

A vacuum leak in your system is a common reason for you to fail an emissions check. Often, you can trace this back to a MAP sensor that is not working correctly. This sensor measures the load of the internal combustion on the electronic control system within the engine. There can also be leaks in the vacuum lines or because of gaskets that need to be replaced.

2. Oxygen Sensor

This sensor measures the level of oxygen in your exhaust gas. A faulty oxygen sensor not only causes extra pollution, but it can also cause overheating and loss of power during acceleration.

3. Fuel Metering

If your fuel metering is out of specification you may end up failing your smog test. This can become an issue when your engine control, carburetor, or fuel injector stops functioning properly.

4. Malfunctioning Ignition System

One part of the smog test will measure the level of hydrocarbons your vehicle is releasing. If the analyzer shows the level to be excessive, you will likely fail your test. High levels of hydrocarbons can usually be blamed on bad spark plugs or spark plug wires. It can also be caused by bad ignition timing or even a worn distributor cap that needs to be replaced.

5. Fuel Ratio Too Rich

Another level that will be measured by the computer at the test is your vehicle’s carbon monoxide levels. If they are found to be too high is can be because the air to fuel ratio is off and you are burning too much fuel, or your ignition is weak. A rich fuel mixture has several causes. Most commonly oxygen sensors, leaking injectors, and too high fuel pressure are likely culprits.

6. Faulty EVAP

Your evaporative emissions system, also known as EVAP, looks after your gas vapors by stopping them from being released into the atmosphere. Instead it redirects the fumes back to your engine. When this system stops working correctly, excessive vapors are detected during your test.

Final Thoughts

Smog tests are regulated state tests that are required by many states to be done routinely while other states do not require this to be done. It is important to check with your local DMV to find out what your requirements are. This is because not getting the smog test done may impede your ability to get your registration done. If you fail the test, you will be given a set amount of time to bring your vehicle to a mechanic to bring it up to compliance. Licensed mechanics can usethe printout you receive at the testing site to help pinpoint the issue and make the process go smoothly.

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