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Why Did My Check Engine Light Come On?

Marc Skirvin
Marc Skirvin

Table of Contents

If you are like most vehicle owners, you may understand little about the check engine light. This illumination comes with no warning and is rarely understood.

For some car owners, it may mean rushing to an auto repair shop. While you might need to eventually take your car to a mechanic for a full inspection, there are a few DIY tricks that can come in handy. This article will discuss what you need to do when you find yourself in that situation.


My Check Engine Light Came On: Now What?

Even if you suspect a minor problem, don’t ignore the warning. This could lead to damage of some car components that could be costly to repair. It could also leave you stranded at your worst moment.

According to a study commissioned by CarMD, over 10% of vehicles on our roads have their check engine light on because the drivers ignored the signal. The study found out that over 50% of the drivers ignore the light for more than twelve weeks.


What the light means

The check engine warning light is a built-in feature within the vehicle’s computer (onboard diagnosis system) that communicates to the driver the malfunctions within the vehicle. The system controls and monitors your car’s performance and adjusts variables such as the fuel mixture, engine speed, and ignition timing. Where there is a malfunction that the OBD cannot rectify, it communicates the feedback to the driver through a warning light.

Besides sending a warning signal, the computer stores the trouble code that provides more information about the malfunction in the car or what triggered the light, for example, a misfiring engine or something as simple as a malfunctioning sensor.

To diagnose malfunctions in your car, you need a code reader. The device is connected to your car’s onboard diagnosis (OBD) system to provide full details. There is a wide variety of inexpensive code readers for DIYers. Some code readers can even switch off the warning light, but you should not take this as a solution to the underlying problem because the light will most likely appear later.


What are some of the common problems?

Depending on the problem, the check engine signal usually remains illuminated or blinks. In most cases, a yellow or orange signal signifies the problem is not serious and may not require immediate attention, but if the light is blinking, it signifies a serious problem that must be urgently addressed.

The following are common malfunctions that can cause the check engine light to come on:

Oxygen sensor failure

An oxygen sensor monitors the quality of unburnt oxygen in your car. It sends the information to the car’s computer, which it will use to control the amount of air and fuel that enters the cylinders. When the Oxygen (O2) sensor is dysfunctional, it means the wrong data is sent to the computer, which makes the engine burn more fuel than it requires.

The end result of this is that your car will be less fuel-efficient and will have more emissions. Besides this, a defective oxygen sensor can also damage other components in your car such as the spark plugs and exhaust system. Most vehicles have two to four O2 sensors, and the code you get from diagnosis usually identifies the dysfunctional one.

The best way to solve the problem is to buy a new sensor and fix it as guided by the user manual. If you don’t replace a defective oxygen sensor, the consequences could be severe.

Faulty gas cap

Most people rarely see a gas cap as an important component, but it is. A cracked or loose cap is another reason that the check engine light could activate. The cap plays a key role in your vehicle’s fuel-delivery system. It helps to regulate the pressure in the fuel tank and seals the fuel system. On top of this, it prevents the escape of gasoline fumes from the fuel tank into the atmosphere.

If the car is handling okay when the check engine signal turns on, the first place you may need to check is the gas cap. While it might not be car-threatening, it is important to have a well-fitting one because it may affect your vehicle’s gas mileage.

Dysfunctional catalytic converter

A catalytic converter is connected into your car’s exhaust system. It converts the carbon monoxide to carbon dioxide, thus protecting the environment. This part usually becomes defective because of neglected maintenance.

If you don’t repair your exhaust system, your car will not pass the emission test. A dysfunctional catalytic converter will also reduce the performance and fuel-efficiency of your car.

Faulty mass airflow sensor

The mass airflow sensor regulates how much air gets into the engine. It communicates with the vehicle’s computer to increase the fuel based on the amount of air getting into the engine. Without it, your vehicle will not adjust to changes in altitude.

With a faulty mass airflow sensor, you may also experience rough idle, unexpected change in the throttle’s location pedal, and trouble starting. A defective mass airflow sensor can damage the oxygen sensors, spark plugs or the catalytic converter.

Old plug wires or spark plugs

Spark plugs seal the combustion chamber and provide gab for sparks to start combustion. The plug wires, on the other hand, transfer the sparks from the coil to the spark plugs. Without these two, the air and fuel mixture in the cylinder will not ignite. It is therefore important to replace them if you notice any wear and tear. Ideally, you should replace spark plugs after every 25,000 – 30,000 miles. Worn out plug wires and spark plugs can cause damage to the ignition coils or the catalytic converter.


How to respond when check engine warning light comes on

Check for any serious problem that may need urgent attention

The first step to take when the light appears is to check the dashboard gauge for indications of overheating or low oil pressure. In most cars, a yellow light means that there’s something that needs to be checked while a red light means that you must stop the car immediately.

Lower speed and load

The moment you notice a blinking check engine signal, decrease speed and find the safest place to stop the vehicle. You should also take your car to a mechanic for a professional checkup.

Tighten the gas cap

For minor malfunctions (when the check engine warning light is yellow or orange), check for potential causes. In many cases, you may find that the gas cap is loose. If that is the case, tighten it and continue with the journey. Please keep in mind that light may take time to reset.

Use built-in diagnostic features

Most modern vehicles come with remote diagnostic features. The feature will help you to decipher the trouble codes.



The check engine alert light tells you something about your car – sometimes in a vague manner, which can complicate things for vehicle owners. If the check engine warning sign comes on, don’t panic; just check for the above possible reasons. The best way to avoid most of the problems is to service your car regularly instead of waiting for the warning signal. After all, the OBD will not warn you that the ball joints are worn or when the water pump has defects. If your vehicle sounds, smells or drives unnaturally, get it checked at an auto repair shop.

This post was contributed by Heather, a freelance writer who creates content based on curiosities that are pertinent to her daily life and the lives of those who surround her. When she’s not contributing as a writer, you can find her connecting with others online as part of her work as an outreach coordinator for a public relations firm.

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About the Author


Marc is the Co-Founder of Cash Auto Salvage and Director of daily operations. He retired from a leading Internet Marketing company in 2013 and has been involved in the automotive industry ever since.

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