Reasons Why My Vehicle Failed its Emissions Test

1 Sep

Reasons Why My Vehicle Failed its Emissions Test

It’s frustrating when your vehicle fails its emissions test. Thankfully, we here at DOC Auto can run a diagnostic check to find out why the vehicle didn’t pass. There are common reasons why automobiles fail emissions tests. Here is what they are for your information.

Check Engine Light

If your check engine light is on, your vehicle will automatically fail the emissions test. This is most likely because you have an underlying problem that is affecting your engine performance. These problems can include a faulty mass airflow sensor or a dead oxygen sensor. The check engine light will also come on if your vehicle’s exhaust system is having problems.

Dirty Air Filter

If you haven’t had your air filter changed in 12,000 miles, it’s possible that this is the reason why your vehicle failed the emissions test. A dirty air filter creates a lean fuel mixture in the combustion chamber and, as a consequence, you end up with more hydrocarbons in your vehicle’s exhaust. It is these hydrocarbons that cause the emissions test failure.

Dirty Motor Oil

Dirty motor oil can also produce more hydrocarbons in your vehicle’s exhaust. In addition, dirty motor oil can damage your engine severely and unnecessarily. It’s important to have your oil changed when your vehicle manufacturer recommends it to make sure that it is always clean and fresh. Otherwise, again, you cause unnecessary damage to your engine and an emissions test failure.

Loose Gas Cap

If your gas cap can no longer create a seal over the gas tank, your vehicle may fail its emissions test and you may end up with the check engine warning. This is because fuel is evaporating out of the tank, which is not only harmful to the environment but also to your health.

Rich Fuel Mixture

A rich fuel mixture can be caused by leaking fuel injectors, a faulty mass airflow or oxygen sensor, or an open fuel pump among other things. A rich fuel mixture means the air and fuel mixture is heavy and fuel. This causes excess hydrocarbons to be released in your vehicle’s exhaust, and, as a consequence, your vehicle will not pass the emissions test.

Spark Plug Problems

Finally, if your spark plugs are old and worn, they may misfire and this will cause your vehicle to flunk its emissions test. Check your owner’s manual to see when you need to have your vehicle’s spark plugs changed, as the mileage duration varies from 30,000 miles to 100,000 miles.

Don’t panic. DOC Auto in Fredericksburg, VA, can help. We’ll find out why your vehicle failed its emissions test and fix the problem.

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Chatham Heights
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Fredericksburg, VA 22405
(540) 899-3732

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Fredericksburg, VA 22408
(540) 710-0173

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