If you live in a state requiring vehicle emissions testing, it might not be on the top of your mind until there’s a problem. But, while many may put off their car’s emissions test, failing to pass this inspection leads to ineligible registration renewal and potentially expensive automotive repairs. And while the world is moving towards zero-emission automobiles, most cars on the road still rely on an internal combustion engine.

That’s why understanding what’s involved with a car’s emissions test and what can cause your vehicle to potentially fail can minimize the stress that may result from testing issues with your state’s requirements.

What Is An Emissions Test?

You may also come across terms like “smog test” or “smog check,” but these are the same thing as an emissions test and are often required to renew your vehicle’s registration in some states. But overall, this test measures the pollutants, como hydrocarbons, carbon monoxide (CO), carbon dioxide (CO2) and others generated by an engine’s combustion process.

The test itself analyzes what comes out of your car’s tailpipe and ensures the exhaust materials meet regulations put in place by the Environmental Protection Agency (EPA) to help reduce air pollution and improve air quality. And while most state requirements match federal specifications, some jurisdictions (like California) have stricter emissions standards. Due to this, it’s important to familiarize yourself with your state’s specific requirements, which you can often find by checking your relevant Department of Motor Vehicles (DMV) website. 

Current emissions testing involves inspecting the car’s on-board diagnostics (OBD), the computerized system that manages pollution controls, and analyzing the exhaust gas. To finish the test, an authorized emissions inspection station uses specialized equipment to check the results and report the information to the state. If your test results say you’ve passed, your vehicle’s registration renewal occurs with no issues; if your vehicle fails, you’ll have to follow mandated steps for getting the vehicle back into compliance. You can even risk potential fines, including possibly paying more than $45,000 per vehicle out of compliance if you’re found breaking the Clean Air Act. 

Generally, you will often receive notification (if applicable) that your vehicle requires an emissions test to renew your registration. For most states, an emissions check will be required either annually or every other year. However, be sure to check your state’s requirements, as there may be exemptions for newer or older cars, diesel vehicles, or hybrid engines. For example, California residents do not need to get an emissions test if their car is:

• Gas-powered and is a 1975 model year vehicle or older
• Diesel-powered and is a 1997 model year vehicle or older OR has a Gross Vehicle Weight of over 14,000 pounds
• Powered by natural gas AND weighs more than 14,000 bounds
• Gas-powered and less than eight model years old
• Is an electric vehicle (EV) 

8 Factors that can Affect Your Car’s Emissions Test

Knowing what can cause your car to fail can help ensure your registration process isn’t at risk if your car requires an emissions test. In fact, there are numerous reasons a vehicle owner may encounter a failed emissions test, with some of the eight most common reasons being:

#1: Defective/Stolen Catalytic Converter

A conversor catalítico is a pollution control device connected to the exhaust system and converts toxic fumes to less-polluting gasses. The apparatus can wear out over time or deteriorate because of corrosion or damage. And because a conversor catalítico uses precious, they’re vulnerable to theft, especially in hybrid vehicles like a Toyota Prius.

mientras un replacement may not be cheap, there are numerous warning signs that the conversor catalítico has seen better days (or may be missing):

• Illuminated check engine light
• Louder-than-normal exhaust noise
• Sputtering engine sound, particularly at start-up
• Weak acceleration

#2 Loose Gas Cap

Keeping enough gas in the tank is important for any gas-powered vehicle, but if you forget to tighten the gas cap when you finish, you could risk your emissions test. A gas cap in a modern vehicle prevents gasoline vapors from escaping into the air, which can harm the environment, and a loose gas cap during an emissions test could cause your vehicle to fail. So after each fill-up, ensure the cap is tightened until a click is heard. But, even a secure gas cap can be a source of problems if its seal has deteriorated. Check that the rubberized gasket inside the cap is smooth and crack-free. 

#3 Old Engine Oil

If it’s been a while since you’ve gotten an oil change for your car, then a failed emissions could be possible. Along with other chemicals, emissions tests measure hydrocarbons emitted during combustion, and past-its-prime motor oil has more hydrocarbons. So, get a jump on things, if needed, with an oil and filter change before having the car’s emissions tested. And if you have an Advantage protection plan from Endurance, you can get breakdown protection while receiving up to $3,500 in yearly maintenance services, including oil and filter changes, to help ensure you’re up to date with your car’s maintenance needs.

#4 Dirty Air Filter

Like a faulty gas cap, a dirty air filter is one of those minor car troubles that can cause big headaches with emissions testing, as a clean air filter helps keep the hydrocarbon count to a minimum. Luckily, like an oil change, it’s usually an easy fix. Check your car’s owner’s manual to learn the recommended air filter replacement schedule and follow it. You may even want to consider swapping out the filter sooner if you find yourself traveling more, especially in areas with dusty roads or highly polluted areas. 

#5 Bad Spark Plugs

Spark plugs have been part of gas-powered engines for more than a century and are essential components that ignite the fuel and initiate the combustion process. But spark plugs can go bad or get worn out, which causes engine misfiring. This inefficiency in the combustion process leads to poorer emissions and a red flag during testing, so be on the lookout for engine hesitation, reduced power, and surging as they are signs of spark plugs needing to be replaced. And like other key information about your car’s maintenance needs, your owner’s manual can be a great place to learn when to replace your car’s spark plugs before they go out. 

#6 Rich Air/Fuel Mixture

Your car’s engine needs the right combination of oxygen and fuel to operate at peak efficiency and with as minimal pollution as possible. A rich mixture, which just means there’s too much gas, is a sure-fire cause of emissions testing troubles. And this can be tied to several issues, including faulty fuel injectors o un bad oxygen sensor in the exhaust system.

#7 Faulty EVAP System

El Evaporative Emission Control System (EVAP) prevents fuel vapors from entering the environment from the gas tank or fuel system. Any troubles will cause a check engine light to come on and trigger diagnostic codes, which may lead to an emissions inspection failure. If you are dealing with an EVAP issue, a repair typically involves the replacement of a charcoal filter canister that absorbs gas vapors.

#8 Illuminated Check Engine Light

While things like a faulty (or missing) conversor catalítico or even a loose gas cap can cause your car’s check engine light to turn on, there are even more issues that can cause the same thing. And regardless of the reason, an illuminated light when getting an emissions test will almost certainly result in a failing grade. And resetting the light won’t make the problem disappear, as the trouble will resurface once the car accumulates enough miles for sensors to capture more data. So if your vehicle has an illuminated check engine light, have a certified mechanic look at it and diagnose and repair the issue before submitting the car to an emissions test. 

Take on Car Repairs with Confidence with Endurance

Owner a car is much more than figuring out how to pass an emissions test; it involves keeping your vehicle in good working condition for as long as possible. But while following your car’s recommended maintenance schedule can help keep it running for longer, it won’t be able to prevent every repair. And for those who have an older, used car past its factory coverage, you’d be on the hook for those expensive repair bills on your own—except when you have an Endurance auto protection plan.

Like your car’s factory-level coverage, Endurance offers you breakdown protection for your vehicle’s most vital components, including the engine, transmission and more, along with other perks and savings that an automaker might not be able to match. For example, Endurance offers a wide range of coverage options, including plans starting at just $79 per month. There are plans for select luxury models, high-mileage cars, and even commercial vehicles. And just by being an Endurance customer, you can enjoy 24/7 roadside assistance, trip interruption coverage and rental car reimbursements to help ensure you’re never stuck with a repair or breakdown. You also won’t find yourself stuck to going to just the dealership for repairs like most automaker-backed plans may have you do. Instead, you’ll be able to take your vehicle to your choice of ASE Certified mechanics o auto repair facilities—including your car’s dealership. And for just a small activation fee, you can enjoy an entire year of Beneficios de élite, including extra perks and savings like tire replacements or repairs, collision discounts and more.

Discover what an Endurance auto protection plan can do for you by requesting a free, no-obligation online quote. Or, if you’d like to learn more about how Endurance can help you, call a member of the award-winning Endurance customer care team at (800) 253-8203. And don’t forget to check out the Blog Endurance for even more articles on topics ranging from expert car care tips, vehicle buying guides, extended warranty comparisons and much more.