Back to all

Why did my vehicle fail its emissions test?

February 23, 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.

Tuffy Cincinnati (Fields-Ertel)
9401 Fields-Ertel
Cincinnati, Ohio 45249
513.683.5060

More articles from Tuffy Fields-Ertel Cincinnati

T for Transmission, T for Trouble (Automatic Transmission Trouble Signs)

February 1, 2026

One of the hardest working components of your vehicle is its transmission, shifting gears up and down when you need it to. The transmission is vital to your vehicle driving properly, and if you start to see signs of problems in it, its best to have them fixed earlier rather than later. (Since ne... More

The Red Menace (How to Deal with Rust)

January 25, 2026

Rust. It's worse if you drive in places that use salt on the roads in winter, or if you spend time driving near a body of salt water. But any vehicle has to deal with rust after years on the road. And it's not just that rust can eat away your vehicle's body and fenders. It can be a real probl... More

Smooth Operator (Shocks and Struts)

January 18, 2026

Few of us ever drive somewhere without encountering some pretty rough roads, and it's amazing how well our vehicles are able to smooth out the ride. Thank your shocks and struts. The two parts are similar. Some cars have shocks in the rear, and struts in the front. Others have struts all around... More