There are lots of reasons for check engine light on. Among all reasons, ‘Loose Gas Cap’ is the most common reason for check engine light. You should check it first. The gas cap blocks the fuel system by maintaining proper pressure in the gas tank. It is essential to check if your gas cap is chipped or cracked. Sometimes, the gas cap remains mild on the fuel system that also can activate the check light. Securing the cap will somehow deactivate the light.

While driving on the road, people often see their check engine light illuminate as a reason to panic. Then, it becomes necessary to inspect your vehicle shortly. I repeat several things that can activate the check engine light, and we should find the specific reason and troubleshoot the problem with a professional. We shall discuss some common reasons for check engine light in this article. Start reading us.


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Common reasons for check engine light

1. Unsuccessful Oxygen Sensor

We have included a loose/cracked/broken gas cap as the significant reason for check the engine light in the introduction. If it is not a gas cap, then a failing Oxygen sensor is the next reason to decline fuel economy. You’ll get accurate data with a diagnostic code reader anyway, or a professional will do it for you. An Oxygen sensor diagnoses unburned oxygen in the exhaust system and plays a vital role in the emissions system.

2. Catalytic converter failure

Like a failing Oxygen sensor, a failing catalytic converter can be a reason for check engine light. Did you ignore several other issues that are related to the catalytic converter? This converter is desegregated to a vehicle’s exhaust system. During the combustion process, it turns carbon monoxide into carbon dioxide. Even if a catalytic converter is failed, it can often be prevented, costing between $200 and $500 depending on the specifications.

3. Spark plug issues

Call it an ignition problem or spark plug issue; they are the same reason for check engine light if failed. An ignition coil does empower the spark plugs with the required electricity and helps the plugs to ignite the fuel and air in the cylinders. Depending on the car’s type, the coil’s number varies, like classic cars have a single-coil, whereas most modern cars contain eight or sixteen separate coils. We have a previous article on how many spark plugs in a V6. Even if one of the single coils does malfunction, it triggers the check engine light. Spark plugs can be worn or fouled and can cause various issues like engine misfire or slow acceleration. Like spark plugs, the worn coils can exhibit the problem. Changing from quality spark plugs will be cheap and easier in the range.

Relevant article: Is It Safe to Drive with Check Engine Light On?

4. Bad spark plug wires

Besides having spark plug and ignition system failure, bad spark plug wires can be a reason for check engine light. Spark plug wires are the main media to transfer electricity from the coil to the spark plug. Without the spark plug wires, it is impossible to make fuel and air mixture inside the cylinder. Most of the cars have a single wire per cylinder, and some have two wires consequently. A bad spark plug wire can also create a rough idle issue, decreased engine performance, and lower gas mileage. Replacing a set of plug wires can cost $50 from your budget. It’s not that high, no?

5. MAF sensor failure

Who doesn’t know about MAF (Mass Airflow) sensor? It monitors correct airflow in the engine as a part of an engine management system. Without it, a car can’t adjust attitude and horsepower. A MAF sensor failure includes engine cranking, rough idle, harsh start, and many more engine problems. You can consult a professional to replace the MAF sensor ASAP, or it will cause reduced gas mileage. It costs between $150 and $200.

6. An aftermarket alarm can cause issues

An aftermarket alarm is luxurious. Still, it makes some reek if not installed correctly. Among all leading side effects, we find draining battery as the most prominent reason preventing your vehicle from starting. Mostly, such a problem triggers the check engine light in the middle of the night. You’ll need to get the alarm fixed if you find it as a reason to check engine light. We recommend doing this replacement with a competent mechanic. Enough to dismiss peace of mind!

7. Common vacuum leak

A car has its vacuum system to perform brake booster, lowers harmful emissions through the engine. If your car starts idling at high rpm, it is the vacuum leak behind it. Like all vehicles’ equipment, vacuum hoses get dried out and cracks as they age. The broken fittings and loose connections can be a source of the leak too. Check engine lights work during a vacuum leak.

8. Battery problem

A vehicle’s battery is as essential as oxygen. I changed my Ford F-150 battery a few days ago. I experienced my car wasn’t starting, lighting up the road with headlights and flickering oncoming traffic. However, we appreciate today’s technology; through this, we get our batteries to last much longer than before. A dead battery can’t be a reason for check engine light, and still, before its death, you’ll find symptoms like a problematic start, engine cranks, and slow acceleration.

What to do if my check engine light is on

What to do if my check engine light is on?

Modern cars are packed with high-tech bells; however, today’s vehicles also have aftermarket devices to identify the reason for check engine light. You can also fix it. Most of the motorists or drivers take their vehicles to the dealership. Spending a few dollars on an OBD II scanner will be the most premium stuff to take.

How to use OBD II to know a specific reason for check engine light?

Start finding your car’s OBD II port. You’ll get it in the driver’s footwall or behind the center console, or in a floor compartment. Plug the scanner and launch the OBD app on your phone. The error codes stored in the car’s ECU appear on the screen. Sometimes, the code seems to be transparent or if it looks critical, go to an expert to figure out if your car needs a repair.

Will the check engine light tell me when to fix my car?

The check engine light illuminates like an idea and indicates something wrong with the car. Yes, the check engine light tells you to go to a skilled mechanic ASAP. You shouldn’t drive long to get your car maintenance done after the check engine light warns you. The check engine light is a check-up reminder for only pricey engine repair. Other functions like water pump, ball joints, and A/C are not involved with the reason for check light.


You must approach car maintenance as a common issue in routine and preventative ways. We have discussed the foremost reasons for the check engine light, and they should be diagnosed for saving engine sounds, smoke smell, and performance. It is essential to change the oil, coolant, and brake fluid after their deadline. Check engine light is necessary to indicate us fixing major car issues.