What Could Cause The Check Engine Light To Come On?


Car dashboards and instrument panels are chock-full of indicator lights that can mean all sorts of things. Thankfully, most of them never turn on when you drive unless there’s a problem that requires your attention. A perfect example is the Check Engine light.

The Check Engine light can mean a long list of different things. However, its most common triggers are a loose or damaged gas cap, worn-out spark plugs, a faulty ignition coil, a problematic catalytic converter, and engine or sensor failures. The light might not seem alarming initially but never take it lightly. Instead, troubleshoot it at home or get the car to a mechanic as soon as possible.

In this guide, you’ll learn plenty more about the common triggers for the Check Engine light. Then, you’ll discover how to troubleshoot the light so you can find the root cause and fix it.

Let’s get started.

Why Is My Check Engine Light Turned On?

There are plenty of reasons why a Check Engine light will illuminate or flash on your dashboard. Unfortunately, it’s not always clear which of those reasons actually triggered the light to turn on.

Still, here are 5 of the most common issues that’ll cause the Check Engine light to come on:

1. Loose Or Damaged Gas Cap

The first reason your Check Engine light might turn on is an issue with the gas cap. More specifically, the gas cap is loose or damaged and doesn’t seal the gas tank correctly.

The gas cap might not seem like a significant component at first, but it actually plays a critical role.

Firstly, it seals your car’s fuel tank and ensures that no fumes can escape. Those fumes are flammable, so keeping them contained with a working gas capreduces the gas tank’s overall fire risk and keeps your vehicle safe.

Besides that, a cap that seals the gas tank correctly also ensures that the fuel system can maintain the correct amount of pressure at all times.

Were the gas cap loose or damaged, the engine would sense that the fuel system’s pressure is incorrect and trigger the Check Engine light that you see.

Read: What is a Hydrolocked Engine and How Bad is It?

2. Worn-Out Spark Plugs

Spark plugs are another set of critical components in any combustion engine. They experience plenty of wear and abuse as part of the engine’s operation, and they can trigger the Check Engine light to turn on once they wear out.

Spark plugs continuously ignite the air and fuel mixture that enters each engine chamber. That process results in explosions that the engine uses to generate power, but it also gradually causes each spark plug to become saturated with oil, fuel, and carbon.

When those things become too saturated, the spark plugs are considered ‘fouled’ and can no longer function efficiently.

Again, the engine can sense that there’s a problem and will turn on its Check Engine light to bring your attention to it.

Read: Dealing With a Car Engine Derate

3. Ignition Coil Problems

The spark plugs described above are powered electrically by a component called the ignition coil. 

The ignition coil acts as a transformer, charging and concentrating the power that comes from the battery. So it can deliver high voltage to each spark plug, thereby triggering the combustion process.

Unfortunately, the ignition coil is another component that can become faulty or fail entirely after being used for many years. With time and regular wear, the ignition coil can’t deliver enough power to the spark plugs as needed.

That, too, will trigger the Check Engine light that you see.

Read: How Much Does It Cost To Rebuild an Engine?

4. Faulty Catalytic Converter

The way air enters the engine is just as important as how it exits after the combustion process happens. After the air and fuel mixture is ignited inside the engine, the gasses from that process exit through the exhaust system.

A section of that system is called the catalytic converter. It’s designed to remove many of the toxic substances in those gasses, making them safer to release out of the vehicle’s tailpipe.

Unfortunately, the catalytic converter can become dirty and clogged over an extended period. That’s especially true if the engine isn’t well maintained and overloads the catalytic converte with more toxic gasses than it can handle.

Sensors will detect the lack of smooth airflow through the exhaust system and tell you by turning on the Check Engine light.

Read: What Does The Service Engine Soon Light In My Car Mean?

5. Sensor Failures 

Lastly, one of the most common reasons your Check Engine light will turn on is a problem with one of its crucial sensors. Typically, that’s the mass airflow sensor, the oxygen sensor, or both.

The mass airflow sensor gauges how much air is entering the engine. That way, the vehicle’s computer can then decide how much fuel to supply to the engine to ensure that the fuel/air mixture is at the correct ratio.

The oxygen sensor, however, is located in the car’s exhaust system. It measures the oxygen levels in exhaust gasses to determine if the fuel/air mixture is burning correctly in the combustion chamber.

As you might have already guessed, a problem at either one of those sensors (or both) will cause the Check Engine light to turn on.

Read: Why Is There White Smoke Coming From The Engine?

How Do I Troubleshoot My Check Engine Light?

As you’ve read above, the Check Engine light will tell you there’s a problem but provide no information as to what that problem might be.

Despite that, you should never assume that light means nothing. If you ignore it for too long, the minor problem triggering it will become bigger, more catastrophic, and more expensive.

So, here’s how you can troubleshoot the Check Engine light in your car:

  • Check your gas cap: When troubleshooting your car, always start with the easiest and quickest thing to rule out. For your Check Engine light, start by inspecting the gas cap to ensure that it’s tight and free from any damage.
  • Refer to other indicators: Look for clues by referring to the other indicators. For example, is the engine’s temperature a little higher than usual? That might mean the engine is overheating, and that’s what’s triggering the Check Engine light.
  • Use onboard diagnostics: Most cars these days have onboard diagnostics. If you have access to a trouble code scanner or reader, you can plug that in and download any active fault codes. Fault codes will identify the problem with pinpoint accuracy, letting you know which system, component, and even which section is affected by the problem.
  • Get to a mechanic: Last, but certainly not least, you should take your car to the mechanic as soon as possible. Firstly, they’ve got diagnostics equipment that can also download the fault codes described above. Your preferred mechanic can find the cause much quicker using their knowledge, experience, and tools. Plus, with your car in the workshop, they can fix the problem immediately and minimize your vehicle’s downtime.

Final Thoughts

The Check Engine light is often treated like a nuisance and simply overlooked. That’s understandable, considering how it doesn’t provide much information at all about why it’s turned on in the first place.

However, you must never take the Check Engine light for granted. If it appears on your dashboard, you should always assume that there’s a critical issue that requires attention.

Don’t worry if you can’t troubleshoot it yourself. Your mechanic will be more than happy to help you with that.

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