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OBD-II and Emission Testing FAQs

Cars use comprehensive computer systems to monitor a vehicle’s engine, transmission and sensors at all times for vital information about your vehicle. And if something goes wrong with your vehicle, the OBD-II system will produce what’s known as a Diagnostic Trouble Code (DTC).

Emission testing is vital in most states in the United States, and it has been a key implementation to ensure that vehicles do not produce too much emissions and pollute the environment.

If you have to have your vehicle inspected and a check engine light is illuminated, you’ll automatically fail inspection. No questions asked.

That’s why it’s so important to have a car health monitor so that you can monitor and correct any potential issues with your vehicle prior to getting it inspected.

So, how important is your OBD-II when having emissions tested? Let’s take a look at some of the most common questions asked when having testing performed.

What is OBD-II?

OBD-II was installed on all vehicles that are 1996 or newer. The system is also found in light trucks, and in diesel vehicles from 1997 onward. The system is a complex computer package that alerts vehicle owners of high emissions.

What Does OBD-II Have to Do With Inspection?

If you’re having an inspection performed, the vehicle will be hooked up to a scanner that will tell the auto emissions testing facilities if the vehicle is producing emissions that are too high.

Note: Some states, such as North Carolina, no longer conduct emissions testing.

What Does a DTC Mean?

If the facility detects a DTC, this means that there’s an issue in the power train/emissions control system. The specific code can be vast, so it’s impossible to say exactly what the code means for your vehicle.

The computer will monitor your vehicle at all times, and codes are logged into the computer so that the mechanic, or in this case, the testing facility, can detect high emissions.

Do I Need to Have My Vehicle Repaired?

Yes. If you have a DTC, this means that you will not pass inspection, depending on the state. You’re not legally allowed to drive without the vehicle being inspected. With that said, you’ll usually receive some kind of paperwork that will extend your inspection deadline for 15 days, or something similar.

The diagnostic center, if it is inside of a repair shop, will often offer to conduct the necessary repairs needed to pass emissions testing.

But you do have the right to bring the vehicle to any mechanic that you wish to have the vehicle properly repaired. A lot of people will go to another inspection station to verify the results if they feel like the original testing facility test was inaccurate.

What’s the Advantage of OBD-II Testing?

When an OBD-II test is conducted, the main advantage is that the computer is able to pinpoint the problem with your vehicle. The code produced is as specific as possible, so it allows for:

  • Faster repairs
  • Less expensive repairs

The OBD-II works as an early problem detection, so when the light illuminates, it will be warning you that there’s an issue early on. When the issue is in the early stages, it’s often more affordable to fix and may even be under warranty still.

Does OBD-II Really Help With Emissions?

Yes and no. The system is designed to tell you when there are issues with your vehicle’s various system. Vehicles have become more emission-friendly, with sensors and other components that will be able to keep emissions under control.

If your engine has an issue, for example, it will not be running as intended by the engineers and performance will be lost.

You’ll likely waste fuel and cause the vehicle to produce more air pollution as a result. OBD-II will be able to detect problems with vehicles that the driver often cannot detect. Emission control deterioration or failure is kept to a minimum in a well-maintained vehicle.

But if you ignore your check engine light or MIL, your OBD-II system will be worthless. Unless you take the warning lights seriously, the system will not help decrease the amount of emissions your vehicle produces.

Can You Just Turn Off the Check Engine Light?

Yes, but that doesn’t mean that the inspection will still pass. You can normally clear out all of the codes by disconnecting the battery cable for 15 –30 minutes. When you do this, your entire car will effectively “reset.”

And there’s a chance that you’ll be able to get the vehicle to the mechanic before the light illuminates.

This doesn’t mean that the light will not illuminate during the test. Your vehicle will start to detect a problem and may store the code early on. When a repair is made, the vehicle may also shut off the light on its own and clear the code if it detects that the problem was fixed.

A mechanic may also reset the dashboard light.

What Can Cause an OBD-II Failure?

An OBD-II failure can be caused by a lot of things, so it’s best to have a code scanner to detect the exact problem with your vehicle. One of many failures that may cause your vehicle to fail emission’s testing:

  • Ignition timing being incorrect
  • Fuel system malfunction
  • Contaminated engine oil
  • Loose or worn gas cap
  • Catalytic converter
  • Air injection system issues
  • Vacuum line issues
  • PCV fault
  • Issues with your exhaust gas re-circulation system

Keep in mind that just because your vehicle doesn’t have a check engine light on, doesn’t mean that you’ll automatically pass your emissions tests. The OBD-II system is just a part of the tests that will be performed, but you may have other emissions testing performed.

We’ve written a lot on the reasons why having your vehicle maintained will be able to extend the lifespan of your vehicle.

The right maintenance will allow you to not only drive safer, but you won’t have to worry about failing inspection, harming the environment or issues with your emissions. When you use a car health monitor to properly keep watch of your vehicle’s performance and potential issues, you’ll be able to repair your vehicle faster and save on potentially future damages a fault can cause.

November 12, 2019


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