Back to all

Why did my vehicle fail its emissions test?

January 19, 2025

We all want to breathe clean air and keep our planet green.  One of the ways to do that is by requiring all vehicles with internal combustion engines to pass an emissions test.  That’s because these vehicles can be big polluters.  

Everyone wants their car to pass the test so they can continue their day-to-day driving routine.  But then comes that one day when they tell you your vehicle has failed.  Why does that happen?

One of the most common reasons is that your gas cap is leaking or loose (or maybe you don’t even have one on your vehicle!).  The gas cap is supposed to seal in vapors, but sometimes its seals or gaskets dry out or crack. Replace it, and you’re good to go.

Another common reason your vehicle failed the test is that your catalytic converter isn’t doing its job. It is supposed to convert toxic gases from your engine into ones that don’t pollute the air.  There are many reasons the catalytic converter may not be working.  It may be physically damaged, or the steady flow of exhaust gases has fouled the converter. 

You may have a bad oxygen sensor. It’s supposed to measure how much oxygen is in your exhaust.  This can cause the air-fuel mixture to be too rich, resulting in too many hydrocarbons in the exhaust. Your ignition system may also have problems, such as worn-out spark plugs.  Dirty fuel injectors can contribute to excess emissions.

Believe it or not, a dirty engine air filter may be the culprit. If it hasn’t been replaced for a while, your vehicle may be emitting too many hydrocarbons -  something that will cause your vehicle to fail the emissions test.

You can usually avoid a failed emissions test by maintaining your vehicle regularly.  The best way to do that is by bringing it to our trained technicians, so your vehicle gets the service it needs, scheduled and non-scheduled.  Plus, you’ll be doing your part to keep our air clean.

Tire Warehouse Depot
250 N. Lapeer Rd.
Lake Orion, Michigan 48362
248-929-0699

Need Service?

Request a Quote

More articles from Tire Warehouse Depot

Gas Smell! (What Causes Gasoline Odors)

June 2, 2025

If you've ever walked into your garage and noticed it smelled like gasoline, pay attention. Gasoline can be dangerous, both from the health problems fumes can cause and the fire danger gasoline presents. There are many things that can cause a vehicle to give off a gasoline odor. One of the easi... More

Why is Air Not Coming Out of My Vents?

May 25, 2025

You climb inside your vehicle, start the ignition, and reach for the fan control for the heating or air conditioning. But when you try to crank it up, no air comes out of the vents. It can make for a very uncomfortable trip, whether its hot or cold outside. Its important for the comfort of you a... More

Timing is Everything (Timing Belt)

May 18, 2025

Talk about exquisite choreography; it happens under the hood of your vehicle every time you take a drive. Your engines many complex parts must work exactly together. One key is a part called a timing belt, which enables the synchronizing of two of your engines components, the camshaft, and the ... More