9 Problems That Could Be Activating Your Car’s Check Engine Light

The check engine light is linked to your car’s computerized systems, which allows it to notify you of minor conditions—such as a loose gas cap or bad spark plug—or serious situations, including a failing catalytic converter or a leaking vacuum system. In many cases, a steady light indicates a minor problem that you can check when you have a chance, while a flashing light indicates a severe issue that should be addressed immediately. Just remember: If you do see that light blink on, it’s always better to address it sooner than later. 

It may not sound like a big deal, but your gas cap keeps your car running properly by keeping the fuel system under pressure. A missing, loose or damaged gas cap allows gasoline fumes to escape, wasting energy, lowering your gas mileage, and resulting in less effective acceleration.

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A car’s spark plugs provide the electric spark that ignites the fuel and air mixture inside the cylinders. Worn or damaged spark plugs can cause numerous engine issues, including misfiring, a rough idle, hesitation during acceleration, and decreased gas mileage.

The ignition coil generates the electricity that spark plugs need to work. A worn or damaged coil can cause the car to shut off unexpectedly, or generate some of the same problems as a bad spark plug, including rough idle, misfiring, hesitation, or decreased gas mileage.

The catalytic converter is an integral part of your car’s exhaust system, and is mandated by federal and state emissions laws. The catalytic converter transforms carbon monoxide (CO), a dangerous byproduct of combustion, into carbon dioxide (CO2) that, while dangerous in its own right, does not have the same immediate health risks as CO. If your catalytic converter fails, your car may run at a higher temperature, will suffer reduced performance and fuel economy, and will not pass required emissions tests.

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Another component designed to reduce harmful emissions is the exhaust gas recirculation valve (EGR), which increases efficiency and lowers the amount of nitrogen oxide that exits the engine. The exhaust gas recirculation system returns hot exhaust gases back to the combustion chamber, thereby warming the fuel and making it easier to burn. The exhaust gas recirculation valve can become clogged over time, leading to poor engine performance, reduced gas mileage and failure to pass emissions tests.

Your car’s oxygen sensor regulates the mixture of air and gas that enters the cylinders. The sensor measures the amount of unused oxygen in the exhaust system, then the computer adjusts the airflow accordingly. Running a car with a bad oxygen sensor will reduce your gas mileage, and can damage other components in your car, such as the catalytic converter and spark plugs. A bad oxygen sensor can also cause your car to fail an emissions test.

This sensor measures the total amount of air entering the engine and determines how much fuel is needed to mix with that air. Problems with the mass airflow sensor can lead to trouble starting the car, a rough idle, stalling, engine hesitation or hiccuping, reduced gas mileage, and sudden changes in the position of the throttle pedal. A bad mass airflow sensor also can damage oxygen sensors, the catalytic converter and the spark plugs.

Many crucial systems in your vehicle rely on the vacuum system, including the air intake, exhaust, and brake boosters. Vacuum hoses can dry and crack as they age, especially in climates where the vehicle is exposed to extreme heat and cold. A bad vacuum system can result in surging idle speeds, rough idle, engine hesitation, hard starting, poor acceleration, and improper transmission shifting.

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Unassuming and simple, these filters keep your car running efficiently by blocking dirt and debris from entering the engine. If the air or fuel filters become clogged, you’ll experience reduced performance and a drop in fuel economy. The car may hesitate, stall, misfire—or it might not start at all. Luckily, this is an easy problem to avoid: Check your car manufacturer’s recommendations for how often to change your filters, and then keep to that schedule.