Why Is Your Check Engine Light On?
You’re driving down the road, not a care in the world, and then you notice something — your check engine light has illuminated. While it is important to inspect your vehicle shortly after the check engine light appears, it may not be a reason to panic. There are a number of reasons why it turned on and several things you can do to troubleshoot the problem before having it checked by a professional.
What Does the Check Engine Light Mean?
The check engine light, also known as the malfunction indicator lamp (MIL), is a warning signal on your car’s dashboard that indicates a potential issue with the engine or emission system. It doesn’t pinpoint the exact problem, but it lets you know something isn’t functioning properly.
The severity of the issue can vary greatly. It could be a minor fix, like a loose gas cap, or something more serious that requires mechanical attention.
Top 5 Reasons Your Check Engine Light Might Be On
While checking your vehicle promptly is important, prioritize finding a safe location to troubleshoot the problem. Understanding the reasons behind the check engine light can help you assess the problem’s severity and decide next steps accordingly.
Here are the top 5 reasons why your check engine light might be on and what to look for:
1. Loose Gas Cap
This is the first item you should check. The gas cap seals the fuel system ensuring proper pressure is maintained in the gas tank. If your gas cap isn’t on tightly or appears chipped or cracked, this could be the reason your check engine light is on. If it’s just not on properly, secure the cap and re-check your dashboard to see if the light turns off. You may have to turn off and then turn back on your vehicle.
2. Failing Oxygen Sensor
If you’re experiencing a decline in fuel economy and your check engine light appears, have your oxygen sensor checked. A professional can check the condition using a diagnostic code reader.
What is an oxygen sensor?
An oxygen sensor measures the amount of unburned oxygen in the exhaust system and is vital to the emissions system.
3. Failing Catalytic Converter
When your catalytic converter is failing it’s usually because you ignored several other issues. These issues are related to other systems that work interdependently with the catalytic converter (spark plugs and wires, oxygen sensor etc.).
What is a catalytic converter?
A catalytic converter is an exhaust containing a catalyst that converts pollutant gases into less harmful ones, like carbon dioxide.
4. Failing Mass Air Flow Sensor
Always have your mass air flow sensor checked when the check engine light comes on. Since many of the parts of the engine work together, when one part fails, others tend to follow suit.
What is a mass air flow sensor?
The mass airflow sensor measures the amount of air entering the engine. It determines how much fuel is required to run your engine efficiently.
5. Damaged Spark Plugs or Wires
Without properly functioning spark plugs, your vehicle will not start. Spark plugs ignite the air/fuel mixture in the combustion chamber of your vehicle. The spark plug wires deliver the spark from the ignition coil to the spark plugs
It’s important to keep in mind that these are the most common reasons for the check engine light to come on; however, there can be other issues that cause the check engine light to illuminate.
What Happens if I Ignore the Check Engine Light?
First, determine if your check engine light is just illuminated or if it is flashing. A flashing check engine light indicates a major internal failure and requires immediate attention. Regardless, do not ignore the check engine light. Continuing to drive with a non-flashing but illuminated check engine light can result in lower fuel economy and eventually lead to more significant and costly repairs. Many of the systems work together, so a failure with one system can cause a chain reaction in performance with the others. If you were to take in your vehicle for state inspection while your check engine light is on, you will fail the emissions test.
A check engine light should always be checked as soon as possible to ensure the integrity of your vehicle. View the Top Driver maintenance checklist to ensure your vehicle runs smoothly from your first destination of the week to your last.
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Frequently asked questions
What does the check engine light actually mean?
The check engine light, officially called the malfunction indicator lamp or MIL, is a warning that your car's onboard computer has detected a potential problem with the engine or emissions system. It does not tell you exactly what is wrong, only that something is not working as expected. The issue can range from trivial, like a loose gas cap, to serious, like a failing catalytic converter. A solid illuminated light means you should investigate soon, while a flashing check engine light means a major internal failure is happening right now and you should pull over and get the car looked at immediately.
What are the most common reasons the check engine light comes on?
Five causes account for most cases. A loose, cracked, or chipped gas cap is the first thing to check, because it breaks the seal that holds fuel-system pressure. A failing oxygen sensor, which measures unburned oxygen in the exhaust, often shows up alongside declining fuel economy. A failing catalytic converter typically results from ignoring other problems for too long, since it works in concert with the oxygen sensor, spark plugs, and wires. A failing mass air flow sensor disrupts the engine's fuel-to-air ratio. And damaged spark plugs or spark plug wires, which deliver the spark that ignites the air-fuel mixture, can prevent the engine from running properly or starting at all.
Can I just tighten my gas cap and ignore the light?
Sometimes, yes. The gas cap is the first thing to check because a loose or damaged cap is a surprisingly common trigger. Tighten the cap until it clicks, or replace it if it looks chipped or cracked, then drive the car. You may need to turn the engine off and back on, and it can take a few drive cycles for the computer to clear the code on its own. If the light goes out, you are done. If it stays on or comes back, the cause is something else and you should have the car scanned with a diagnostic code reader to identify the actual fault.
What is the difference between a solid and a flashing check engine light?
A solid illuminated check engine light means the system has detected a problem that needs attention but is not an immediate emergency. You can usually drive to a safe location or a repair shop, but ignoring it can lower your fuel economy and snowball into bigger, more expensive damage over time. A flashing check engine light is a different story, it indicates a major internal failure such as an active engine misfire that can destroy the catalytic converter in minutes. If your light is flashing, reduce speed, get off the road safely, and have the car towed rather than driven to a shop.
What happens if I just ignore my check engine light?
A few things, none of them good. Fuel economy will usually drop, sometimes noticeably, because the engine is running outside its optimal range. Small problems compound: a bad oxygen sensor leads to a wasted catalytic converter, a worn spark plug leads to a misfire that damages other components, and so on. You will also fail any state emissions or safety inspection while the light is on, which can block your registration renewal. Top Driver's maintenance guidance is simple: get the code read as soon as it is convenient, fix what is actually wrong, and you will spend far less than you would on the cascade of failures that follow neglect.
