Why did my vehicle fail its emissions test?
April 6, 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.
Sterling Tire & Auto
34701 Van Dyke Rd
Sterling Heights, Michigan 48312
586-264-7775
Need Service?
More articles from Sterling Tire & Auto

Losing Your Cool (Why is My Air Conditioning System Not Working?)
January 25, 2026
When you turn on the air conditioning in your vehicle, you expect cool air to come out of the vents. You depend on it, especially in hot weather, but it can also be important in humid weather when you need it to help defrost your windows and windshield. The air conditioning system has a lot of p... More

Why Maintaining Your Windshield Wipers and Washers Matters (Windshield Wiper and Washer Inspection)
January 18, 2026
What do mud, bird droppings and frost all have in common? When theyre covering your windshield, they can temporarily obscure your view of the road, leaving you driving blind. And when you cant see the road clearly ahead of you, it can be really scary. Thats one of the reasons its important to m... More

Why is My Brake Pedal Hard to Push?
January 11, 2026
When you push on your brake pedal, you should find your vehicle easy to stop. But at some point, you might notice stopping takes much more pressure on the pedal than it used to. When it gets to that point it becomes a safety issue, and you should bring your vehicle in so we can track down whats... More
