If you live and drive in California, you're likely subject to a periodic smog inspection. Many counties require you to obtain a current smog certificate (this certifies that your vehicle isn't leaking harmful pollutants into the atmosphere and contributing to air quality problems) before obtaining your vehicle registration. However, a number of fairly minor issues can cause you to fail a smog inspection, making it illegal to operate your vehicle until you've had repairs made and a certificate obtained. Read on to learn more about how you may be able to avoid last-minute smog problems.

What are some common reasons a vehicle may not pass a smog inspection?

The smog inspection primarily focuses on the emissions system, ensuring that your vehicle is up to date on all federal and state emissions standards. High emission volume of the particulates that make up vehicle exhaust are one of the key contributors to environmental smog, a harmful airborne substance that can aggravate allergies and asthma for sensitive individuals. Your emissions system filters potentially harmful substances out of your vehicle's exhaust. However, problems like a faulty oxygen sensor (which regulates the air to fuel mixture in the combustion process) can cause your vehicle to burn excess fuel, overloading your emissions system and leaking pollutants into the air.

Other emissions problems can include clogs or malfunctions within the catalytic converter and fouled spark plugs. Any issues that affect your vehicle's ability to burn fuel at the appropriate rate can have a negative effect on your emissions system. If you undergo a smog inspection, the inspector will point these problems out so that you won't need to spend money on diagnosis.

What if you can't afford the needed repairs?

There are some exemptions that may be available that can allow you to pay your registration without passing a smog inspection. If your vehicle is 6 years old or newer, you don't need a certificate yet -- and if you move to California with a vehicle 4 years old or newer, you also won't need a smog inspection. And in most cases, you'll be permitted to pay your vehicle's registration (even without a smog certificate) to avoid any late fees or penalties.

However, if your vehicle has emissions problems, it's likely that it is also burning more fuel than necessary. It's important to repair these issues to prevent further problems down the road. If you don't think you can afford the repairs needed to bring your vehicle up to code, there may be financial assistance available. Certain low-income individuals can qualify for up to $500 toward needed repairs or $1,500 if you choose to "retire" or scrap your vehicle instead. Talk to a mechanic should you need a smog inspection.