Top 12 Reasons Your Check Engine Light is On
Posted on November 29, 2021
We’ve all been there—driving along when suddenly that little yellow check engine light pops on. Whether it's your first time seeing it or you’ve been through this before, it's always a bit unsettling. You might wonder, "What’s wrong now?" or consider ignoring it for a while.
However, you need to understand that while a steady yellow light usually isn't an emergency, it’s still a sign that something needs attention soon. That said, if the light is flashing, it’s more urgent and should be checked right away to avoid bigger issues.
Typically, the check engine light is related to your vehicle's emissions system. In this blog post, we’ll explore the top 12 reasons why your check engine light is on. Knowing these common triggers can save you time, money, and the hassle of unexpected breakdowns.
1. Lose Gas Cap (Not On Correctly Or Broken/Damaged)
A loose or damaged gas cap might seem like a minor issue, but it’s actually one of the most common reasons for your check engine light to come on. The gas cap plays a crucial role in maintaining the correct pressure within your car’s fuel system by keeping it airtight.
When the cap isn’t properly tightened or if it’s broken, fuel vapors can escape, causing the system to detect a problem and trigger the warning light. This is often the easiest and least expensive fix for a check engine light. If the cap is simply loose, tightening it might turn off the light after a short drive.
However, if the cap is damaged, you’ll need to replace it—an affordable solution that varies in cost depending on your vehicle. Taking a moment to check your gas cap could save you a trip to the mechanic.
2. Oxygen Sensor Failure
The oxygen sensor in your car plays a vital role in ensuring your engine runs efficiently. It measures the level of unburned oxygen in the exhaust and sends this information to your car's computer, which then adjusts the fuel-to-air mixture for optimal performance.
If the sensor fails, the computer can’t make these adjustments properly, leading to poor fuel economy and increased emissions.
When the oxygen sensor is faulty, your check engine light will likely turn on, signaling the need for a replacement. Ignoring this issue can result in further engine problems and higher fuel costs, so it's important to address it promptly.
3. Catalytic Converter Failure
This essential component in your vehicle's exhaust system converts harmful gases like carbon monoxide into less harmful emissions. While catalytic converters are generally reliable, they can fail due to age, underlying engine issues, or a buildup of contaminants.
Unfortunately, replacing a catalytic converter can be expensive, typically ranging from $200 to $600 depending on your vehicle.
Preventing catalytic converter failure is possible with regular maintenance. Timely oil changes and occasional highway driving can help keep it in good condition, especially if you mostly drive short distances in the city.
If you notice unusual noises or smoke from your exhaust, it’s a good idea to get your catalytic converter checked out to avoid costly repairs.
4. Faulty Spark Plugs or Wires
Spark plugs and wires play a key role in igniting the fuel in your car’s engine. If either component is faulty, it can lead to poor engine performance, slow acceleration, or even engine misfires. When this happens, your check engine light may turn on as a warning.
To avoid these issues, you must regularly inspect and replace your spark plugs and wires. Ignoring them can lead to bigger problems, such as poor fuel efficiency or difficulty starting your car, so keeping them in good condition ensures your engine runs smoothly and efficiently.
5. Faulty Ignition Coil
If the ignition coil becomes faulty, it can lead to problems like difficulty starting your car, misfires, or reduced acceleration. When this happens, the check engine light will likely come on to alert you of the issue.
Addressing a faulty ignition coil promptly is important because ignoring it can lead to more severe engine problems over time.
Fortunately, replacing a faulty ignition coil is usually a simple and affordable fix, keeping your engine running smoothly and efficiently. Regular maintenance checks can help catch this issue early and keep your vehicle in top condition.
6. Mass Airflow Sensor Failure
The mass airflow sensor plays a critical role in your vehicle by measuring the amount of air entering the engine. This information is sent to the car’s computer, which adjusts the fuel injection to ensure the engine runs smoothly.
When the mass airflow sensor fails, it can disrupt this balance, leading to problems like poor fuel efficiency, rough idling, or even difficulty starting the engine.
If left unchecked, a faulty sensor can strain the engine and potentially cause more serious damage over time. If you notice any of these symptoms, get the sensor checked and replaced if necessary to keep your vehicle running efficiently.
7. Issues with an Aftermarket Alarm
An aftermarket alarm system can sometimes cause more trouble than it's worth, especially if it’s not installed correctly. Poor installation can lead to several issues, including battery drainage, triggering the check engine light, or even preventing your vehicle from starting.
Additionally, these alarms might go off unexpectedly due to minor disturbances, like a leaf falling on your hood, leading to frustration and potential damage.
If you’re experiencing problems with your aftermarket alarm, you must have it inspected by a qualified mechanic. They can fix, reinstall, or replace the system to ensure it works properly and doesn’t interfere with your vehicle’s performance. While a proper installation might cost a bit more upfront, it ensures that your alarm functions as intended.
8. Exhaust Gas Recirculation Valve Failure
The exhaust gas recirculation (EGR) valve is crucial for reducing harmful emissions by redirecting some of the exhaust gases back into the engine. This process helps improve fuel efficiency and lower pollutants.
When the EGR valve fails, it can disrupt the air-fuel mixture, leading to higher emissions, decreased engine performance, and poorer fuel economy. You might notice symptoms like engine knocking, rough idling, or sluggish acceleration.
To address EGR valve issues, technicians use advanced diagnostic tools such as OBD-II scanners and digital multimeters to pinpoint the problem. Depending on the diagnosis, they may clean the valve, replace any faulty parts, or install a new EGR valve to restore your vehicle’s performance and efficiency.
9. Low Fluid/Oil Levels
Low fluid or oil levels can significantly impact your vehicle’s performance. Essential fluids, including engine oil, transmission fluid, and coolant, are crucial for keeping your engine running smoothly.
If any of these fluids drop below their recommended levels, it can cause your engine to:
- Overheat
- Shift poorly
- Even suffer damage
This can trigger your check engine light and signal a need for immediate attention.
To prevent these issues, regularly check your fluid levels and top them off as needed. Refer to your vehicle’s manual for the correct fluid types and levels. If you notice the check engine light on, check your fluid levels first.
10. Electrical Issues
Modern vehicles depend on intricate electrical systems to operate properly, including components like:
- dead battery
- Electrical systems
- Electronic systems
- failing battery
- malfunctioning electrical accessories
If there’s an issue with any of these electrical systems, it can trigger the check engine light. Common problems include a failing battery, a malfunctioning alternator, or issues with wiring and connections.
To address these issues, you must have a professional perform a diagnostic test using a check engine light reader. This tool can pinpoint the exact problem and help prevent potential breakdowns or more severe damage.
11. Worn-Out Timing Belt
This synchronization is essential for smooth engine operation and optimal performance. When the timing belt becomes worn or damaged, you may notice symptoms like:
- Engine misfires
- Unusual noises
- Check engine light warning
Ignoring these signs can lead to severe engine damage, as a broken timing belt can disrupt the engine’s timing and cause costly repairs.
To prevent these issues, it’s important to follow your vehicle’s maintenance schedule and replace the timing belt at the recommended intervals.
Regular inspections by a trusted mechanic can help identify wear and tear early, allowing you to address any problems before they lead to more serious engine damage.
12. Loose or Damaged Exhaust Pipe
A loose or damaged exhaust pipe can trigger your check engine light and create noticeable issues in your vehicle. If you hear a hissing or rattling noise from the exhaust system, it might indicate a problem with the exhaust pipe.
A damaged pipe can result in increased emissions and reduced fuel efficiency, affecting both your vehicle's performance and your wallet.
To address this issue, have your exhaust system inspected by a professional as soon as possible. They can identify any leaks or damage and perform necessary repairs or replacements. Prompt attention to a faulty exhaust pipe can prevent more extensive damage and avoid costly repairs down the line.
My Check Engine Light Is On—Now What?
If your check engine light comes on, it’s best to head straight to the dealership, but if you’d like to know more before you head over, consider buying an OBD II scanner, which typically costs less than $40.
This device plugs into your car's OBD II port—usually located in the driver’s footwell—and retrieves error codes from your vehicle’s computer.
Once you have the codes, you can look them up online or in a repair manual to get an idea of the issue. Keep in mind that while these codes provide useful information, they might not give you the full picture. Sometimes, further investigation is needed to pinpoint the exact problem. Make sure to choose a scanner compatible with your car’s make and model.
Will The Check Engine Light Tell Me When I Should Fix My Car?
The check engine light can indicate a range of issues with your car, but it doesn’t replace regular maintenance or a mechanic’s expertise.
It’s not designed to tell you when to perform routine tasks like changing the oil or checking the coolant levels. Instead, it signals that something needs repair, often after damage has already occurred.
Think of car maintenance as having two parts: regular preventative maintenance and responsive diagnostics. Stick to a schedule for routine tasks to avoid surprises and pay attention to any new noises or issues that arise.
How To Reset the Check-engine Light?
Diagnosing the problem and correcting it will reset your check-engine light. You can also use an Engine Fault Code Reader/Scanner to reset the light manually. However if the issue causing the warning to be triggered has not been solved, the light will reappear.
Schedule Maintenance with CarHub Today
At CarHub, we keep your vehicle running smoothly and safely. If your check engine light comes on or you have any concerns about your car’s performance, don’t hesitate to contact us. Our Service Advisors are here to help diagnose any issues and guide you through the next steps.
To ensure your vehicle remains in top condition, schedule regular maintenance with us. Whether you need an inspection, repair, or just have questions about your car’s care, we're here to assist you.