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Why Is My Check Engine Light On? Reasons, Tips, & FAQ

check engine light

The check engine light on the dashboard of a car is one of the ways that a car’s internal diagnostic system can inform you of problems. It’s beneficial and, while it can spell bad news, it doesn’t necessarily mean that your engine has completely gone. Unfortunately, it doesn’t provide the most comprehensive review of your engine, either, with the only real information it can provide being that there is a problem.

Read on to find out what it means when the light is flashing or illuminated permanently and what the possible causes of a check engine light are.

car and road divider

Flashing Or Static?

Typically, a check engine light can either be flashing or static. A static light that is always on and doesn’t blink indicates that a potential problem has been found. If the light is static, it doesn’t necessarily mean you have to pull over and get help straight away.

You should be OK to continue your journey and have your engine checked when possible. If the light is blinking, however, this is a sign of a major problem and it means that you should pull over and call for assistance as soon as possible. Continuing to drive with a blinking check engine light could result in serious and expensive repairs being needed.

Check Engine Light Indicator
Image Credit: Daniel Krason, Shutterstock

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The check engine light means that there is a potential problem or a definite problem with the engine. Beyond this very vague description, the light can’t tell you much more on its own, and there are a host of possible causes.

O2 Sensor Failure

The O2 sensor or oxygen sensor measures oxygen levels in the exhaust system. If the sensor is damaged or inoperable, the engine won’t be able to properly regulate the right mixture of air and fuel that is sent to the cylinders. The car will keep running with a damaged O2 sensor, but it will use more gas. If left for too long, it can lead to more serious problems.

Loose Fuel Cap

This is potentially one of the easiest problems to fix. It is caused when the fuel cap isn’t properly replaced on the fuel tank. You possibly didn’t replace the cap after filling up, or there may be some debris in the screw thread or connector. Alternatively, if the cap is damaged or broken, it will need replacing, but this is a relatively inexpensive repair, at least when compared to a total engine rebuild.

gasoline into car fuel tank
Image Credit: Piqsels

Faulty Catalytic Converter

The catalytic converter turns potentially dangerous carbon monoxide into carbon dioxide. The part itself is found in the exhaust system and while it is a simple mechanical fixture, it can cost several hundred dollars to replace. If it is a problem with the cat, you will likely see dark smoke coming from the exhaust and a rattling noise as you drive.

Spark Plug Problems

Spark plugs give the spark that is needed to fire the cylinders in the engine. When there is a problem with a spark plug, your car may continue to run and the ignition may work as expected. However, you are more likely to suffer misfires and you may notice a lack of power or other inconsistencies with performance. A spark plug may need cleaning or replacing. It may also be the case that the spark plug wires need replacing. Wires are slightly more expensive than plugs but shouldn’t set you back more than $60 or so.

Replacement of the spark plug of lawn mower_Alexsander Ovsyannikov_Shutterstock
Image Credit: Alexsander Ovsyannikov, Shutterstock

MAF Sensor Failure

The Mass Airflow Sensor, or MAF, determines how much air is being sent to the engine. The car will idle loudly and may misfire. You may also notice a change in the throttle pedal position and your fuel consumption will go up. Repairs are relatively inexpensive, and you should get this problem fixed before it causes further damage.

Vacuum Leak

The vacuum system in a car helps reduce emissions and also plays a part in the braking system. If your car idles at high revs, it could be a sign of a vacuum leak. Most often, the problem is with the vacuum line rather than the vacuum unit itself, but this can be difficult to locate, so while the line is inexpensive to buy, having a mechanic or engine diagnostic company locate the problem means that the costs soon add up, unless they are fortunate and find the leak straight away.

Image Credit: IgorShubin, Pixabay

EGR System Failure

The Exhaust Gas Recirculation, or EGR, system reduces nitrogen oxide emissions. It helps the engine run smoothly and efficiently by pumping hot gases back into the engine. The hot gases make it easier to ignite the fuel, but the valve can get clogged and may completely fail. If it is only clogged, the valve can be removed, cleaned, and replaced, otherwise you will need to buy and fit a replacement.

Dead Battery

If your car battery is dead, you will notice when your car won’t start or even try to start. When this happens, the check engine light also comes on. Check the connections, consider charging or trickle charging the battery, or buy a replacement battery. Replacing a battery yourself is usually an easy job, but some modern cars, especially compact cars, can make it difficult to easily access the battery itself so you may need to get professional assistance.

signs and symbols of a car battery
Image Credit: kaboompics, Pixabay

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The check engine light provides a warning that something may be wrong with the engine or one of the components of your engine. It isn’t necessarily a catastrophic failure, but it could be a sign of a bigger problem and is always worth investigating. If the light is blinking, this does mean that something major is wrong and you will need to have the engine seen to. The exact problem can vary from a dead battery or spark plug to a failed catalytic converter.

Featured Image Credit: virgmos, Shutterstock


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