Is Your Check Engine Light On? Discover the Top 10 Culprits

While your car can’t have a conversation with you, it does have its ways of communicating. Chimes, icons, and messages serve as its language. Among these, there’s one icon you should never ignore: the orange, engine-shaped one found in the instrument cluster. This icon illuminates when the car’s onboard computer detects a problem.

Now, don’t panic if you see it. Seeing the check engine light doesn’t necessarily mean you’ll have to empty your wallet at the nearest mechanic. In fact, some issues triggering this light are quite basic and can be quickly fixed. However, ignoring the light is not advisable. It’s important to get the problem checked out as soon as possible.

So, here are the 10 most common reasons your check engine light may turn on. Remember that the fault code causing the light to appear is stored in your car’s onboard computer. By using a simple device, you can retrieve the code and get a precise idea of what’s wrong under the hood. This DIY approach will save you money in the long run.

Oxygen Sensor Failure

Oxygen sensor
The oxygen sensor (also known as O2 sensor) measures the amount of unburnt oxygen in your car’s exhaust system. It relays this data to the vehicle’s computer, which uses it to regulate the air-fuel mixture entering the cylinders. While your engine will continue running despite a faulty O2 sensor, it will consume more fuel than usual. In the long term, this could lead to damage to components like spark plugs and the catalytic converter. Additionally, it may cause your car to fail an emissions test. The average cost of a quality oxygen sensor is around $175, but remember that most late-model cars have more than one.

Loose Fuel Cap

John Wolf/123rf
Believe it or not, a loose fuel cap is one of the most common reasons for the check engine light to come on. This cap is a vital part of your car’s fuel delivery system. It prevents gasoline fumes from escaping the fuel tank and helps maintain the correct pressure in the system. So, if your check engine light turns on right after a refuel, pull over and ensure the cap is securely tightened. Sometimes, the cap may need to be replaced, but don’t worry, it won’t break the bank. You can find universal-fit gas caps at most auto parts stores for around $15.

Catalytic Converter Failure

Catalytic converter failure
The catalytic converter is an essential component of your car’s exhaust system. It converts the carbon monoxide produced during combustion into carbon dioxide. While this part is relatively simple, failure to maintain it can be costly. A new catalytic converter can cost between $200 and $600, depending on your car’s make and model. Regular maintenance, such as timely oil changes, is crucial to keep it functioning properly. If you mainly drive short distances in the city, take your car on the highway occasionally to prevent clogs. Additionally, be attentive to unusual sounds or discolored smoke emerging from the exhaust.

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Spark Plug/Ignition Coil Issues

Spark plug
To put it simply, an ignition coil generates the electricity needed by spark plugs to ignite the fuel and air mixture in the cylinders. While classic cars have a single coil, modern vehicles often have one coil per cylinder or a coil pack powering multiple cylinders. Malfunctioning ignition coils almost always trigger the check engine light. Worn or fouled spark plugs can cause engine misfires and hesitation during heavy acceleration. A quality spark plug costs between $10 and $20, while a coil is generally around $50.

Bad Spark Plug Wires

Spark plug wire
Spark plug wires transfer electricity from the coil to the spark plug. The fuel and air mixture in your car’s cylinders rely on them for ignition. Most cars use one wire per cylinder, though some older models have two wires per cylinder. It’s important to note that most newer cars don’t use spark plug wires. Symptoms of faulty wires include a rough idle, decreased engine performance, and lower fuel efficiency. Replacement wire sets typically cost around $50, and you can easily replace them without any special tools or knowledge.

Mass Airflow Sensor Failure

Mass airflow sensor failure
The mass airflow (MAF) sensor monitors the amount of air entering your car’s engine. It’s an integral part of the engine management system, allowing your vehicle to adjust to changes in altitude. Signs of MAF failure include a rough idle, difficulty in starting the engine, and sudden changes in throttle response. Reduced gas mileage and stalling can also indicate a problem with the MAF. The cost of a late-model MAF ranges from $120 to $150.

Issues with an Aftermarket Alarm

Car alarm
An improperly installed aftermarket alarm system can cause havoc in your car. It may drain the battery, trigger the check engine light, or even prevent your vehicle from starting. And just when you least expect it, that alarm might go off in the middle of the night because a leaf dropped on the hood. If you’re experiencing any of these issues, consult a competent mechanic to fix or reinstall the alarm. While getting it done correctly may cost a bit more, the peace of mind provided by a fully functional alarm is priceless.

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Vacuum Leak

Car vacuum hoses
Every car has a vacuum system with various functions. The brake booster relies on vacuum pressure, and the system helps reduce emissions by routing gasoline fumes through the engine as they evaporate. A surge in idle speed or an unusually high rpm can be signs of a vacuum leak. Vacuum hoses can dry out and crack over time, especially when exposed to extreme temperatures. This is the most common cause of such leaks. Other issues, like cracked fittings or loose connections, can also contribute. Vacuum lines are inexpensive, but finding the leak can be time-consuming and costly if you don’t do the work yourself.

Exhaust Gas Recirculation Valve Failure

Exhaust gas recirculation valve
The exhaust gas recirculation (EGR) system reduces the amount of nitrogen oxide emitted by your car’s engine, improving its efficiency. By directing hot exhaust gases back into the combustion chambers, it helps enhance fuel combustion and reduce emissions. The EGR valve can become clogged or fail outright. If you have a basic understanding of mechanics, you can remove, clean, and reinstall the valve in a relatively short time. Replacing a faulty valve may cost around $125 for a brand-new, high-quality unit.

Dead Battery

Dead battery
The battery is a critical component for your car’s start-up. Without it, your car won’t come to life. Fortunately, modern batteries are durable and maintenance-free. The cost of a new battery varies depending on your vehicle’s type, but expect to spend at least $100 for a quality battery. While changing or charging a battery yourself is relatively simple, keep in mind that some newer cars have complicated battery placements. Also, disconnecting the battery will oftentimes reset your stereo system. Make sure you have the radio code before disconnecting the terminals, or you’ll be driving in silence.

My Check Engine Light is On. What Should I Do?

Modern cars are packed with advanced features, yet you’ll still need an aftermarket device to decode the check engine light. Many drivers opt to take their cars to the dealership, but this is the most expensive option. Instead, consider investing in an OBD II scanner or a more advanced adapter. These devices are affordable, with prices starting under $40. The scanner plugs into your car’s OBD II port, usually located in the driver’s footwell and not too far from the hood release. Once connected, the scanner will display the error codes stored in your car’s ECU. While some codes are self-explanatory, others may require a bit of research. Repair manuals and online resources are helpful for interpreting codes. A word of caution: error codes are handy, but they don’t always tell the whole story.

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Let me share a personal experience to illustrate this. Once, while working on a relative’s car that had lost all power, the ECU codes indicated a turbo problem. However, upon closer inspection, it turned out to be a cracked vacuum hose. So, having a list of codes won’t always provide an immediate solution. Sometimes, you may need to spend a few minutes (or occasionally a couple of hours) exploring the engine bay to locate the root cause. Professional-grade code scanners are more precise but significantly pricier. Remember, a scanner provides codes, but you’ll need an understanding of what each code means or the means to find out. Some auto parts stores offer free diagnostic tests, but having your own scanner saves time, money, and enhances your car knowledge. Ensure your chosen scanner is compatible with your specific make and model by doing thorough research.

Will the Check Engine Light Help Me Determine When to Fix My Car?

The check engine light provides an idea, sometimes more precise and other times more vague, of what’s wrong with your car. However, it does not replace the expertise of a skilled mechanic or routine maintenance.

Don’t wait for the check engine light to come on before getting your car serviced. Your car’s ECU won’t alert you when the water pump is about to fail, when a ball joint is worn, or when your A/C will stop cooling in the middle of August. Many people mistakenly believe that the check engine light serves as a reminder for general maintenance, but in reality, it signals the need for repairs. By the time it illuminates, damage has often already occurred.

Maintaining your vehicle involves two steps. The first is routine preventative maintenance, consisting of scheduled tune-ups, designed to prevent issues from arising. The second step is responsive diagnostic maintenance, which addresses changes in how your car sounds, smells, or feels as you drive. Familiarize yourself with your car’s basic needs, such as oil and coolant changes or brake pad replacements. Simple research on your specific vehicle and basic mechanics can save you time and money in the long run. By establishing a regular maintenance routine, you may never see that little orange engine light come on at all.

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