The Many Reasons Why Your Check Engine Light Is On

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check engine light on

The check engine light turning on is one of a car owner’s biggest nightmares. This is a sure sign that there is something wrong beneath the hood of your automobile, and it’s difficult to tell how severe those issues are. Almost all of us have been there; it’s a situation we’ve all experienced. Regardless of whatever the color of the light is yellow, red, or orange, it’s almost always followed by a feeling of worry, tension, or annoyance.

The Check Engine Light or CEL on your dashboard is always not a good sign for your vehicle. At the very least, something as straightforward as a loose gas cap or as complicated as a faulty sensor, cabling, connection, or even a more serious engine issue.

Overlooking it if the automobile is running might seem logical for a short period, but the problems will continue to accumulate. In this article, we’ll go over what the check engine light means and the several reasons why such warning lights come on.

What Is The Check Engine Light?

The check engine light is a component of what is known as the onboard diagnostics (OBD) system in your vehicle. Computers and electronics have progressively regulated and supervised car efficiency since the 1980s, directing factors such as the Engine Management System (EMS) managing the fuel mixture, ignition timing, and engine speed. Additionally, a computer directs the automatic gearbox to shift gears in current automobiles.

When a computer detects an issue with the electronic control unit (ECU) that it is unable to resolve, it illuminates a warning light called “check engine,” “check powertrain,” or “service engine soon.”  Alternatively, these warning lights may simply be an image or icon of an engine, possibly with the caption “check” or the whole phrase that reads “check engine.”

Along with the light switching on, the car’s computer database system records a “trouble code” that specifies the cause—issues such as a faulty sensor or as bad as a misfiring engine. The trouble code can be scanned with an electronic scan device or a diagnostic computer, often called an OBD scanner; these devices are standard equipment in auto repair shops. Additionally, there are a variety of reasonably inexpensive code readers or scanners intended for DIYers.

Reasons Why Your Check Engine Light Is On

Sometimes, your car’s check engine light may illuminate when it’s time for routine car maintenance, which is not to worry about. However, the following are the typical causes of a vehicle‘s check engine light to illuminate in most cases. Always remember that fault codes that triggered the light are recorded in your vehicle‘s onboard computer and can be obtained with an OBD scanner’s diagnostic test to precisely determine what’s happening underneath the hood.

Faulty, Missing, or Loose Gas Cap

Your car tank’s gas cap is a component of a complete, closed container that recirculates fuel fumes from the fuel tank and prevents them from leaking into the atmosphere. As a result, this system of pipes and valves is constantly maintained, and a critical component of this structure is the gas cap. If you mistakenly left the fuel cap open, you’ll notice this warning light quite fast.

These fuel tank recirculation, aka “EVAP emission control” system leakage, is often classified as “large” or “small” leaks. It’s essential to remember that the leak is usually not caused by the gas cap; it might be any of the plastic recirculation pipes, couplings, or connections; however, on most occurrences, the gas cap is frequently the cause.

Faulty Oxygen Sensor

Oxygen sensors have a harsh existence at +800 degrees of the vehicle‘s exhaust system temperatures and are inclined to fail after 80,000 miles. Combustion involves an exact combination of chemical gasses. The oxygen sensor continuously analyzes these gases to ensure a sufficient oxygen supply. When the oxygen sensor malfunctions, the car is unable to function correctly.

This substantially affects fuel efficiency and may result in thousands of dollars in damage. Replacing the oxygen sensor as soon as possible can spare you time, effort, and money on avoidable repairs.

Bad Mass Airflow (MAF) Sensor

The mass airflow sensor monitors the quantity of air reaching the engine and calculates the fuel volume required to function the engine correctly. When there are leaks in the intake manifold before or after the MAF sensor, the check engine light may illuminate. Mass airflow sensors are dirt, water, and oil sensitive, and any pollution on them might cause a warning light to illuminate.

Cleansing the sensor using an intake cleaner/mass airflow sensor cleaner will sometimes resolve the problem. Occasionally, the mass airflow sensor merely needs to be changed. Ensure that the intake duct is thoroughly inspected for damages like tears, rips, and leaks.

Catalytic Converter Failure

By turning toxic carbon monoxide into carbon dioxide, the catalytic converter helps safeguard the atmosphere. The downstream oxygen sensors closely check the catalytic converter’s operation, and if anything goes wrong, a variety of diagnostic trouble codes depending on “Catalyst efficacy” will display. It’s critical to remember that the catalytic converter is unlikely to malfunction independently.

Usually, something leads the catalytic converter to fail or function poorly. As a result, simply changing the oxygen sensors or converter surrounding it often does not resolve the issue and frequently fails the replacement converter. A blown head gasket, for example, might drive burnt coolant vapors into the exhaust, producing a catalyst code and turning on the check engine light.

Engine Misfires

The spark plugs ignite the air/fuel mixture in your car’s combustion chamber; however, if the sequencing of the spark, the mixing of the fuel, and the compression of the air aren’t precise, you may have a misfire. Numerous faults may result in a misfire on one or more cylinders. Below are the causes of misfire that can illuminate the check engine light.

Defective ignition coil

The ignition coil creates the electrical current required by the spark plug to spark the air/fuel mixture within the cylinders. While classic automobiles utilize a single-coil, many modern cars employ one coil each cylinder; this is sometimes referred to as a coil pack. Suppose a V8 engine powers your vehicle; it could utilize eight different coils. Regardless of how many ignition coils your car has, when the check engine light illuminates, it’s probably caused by a faulty ignition coil. However, keep in mind that if your automobile runs on diesel, that implies your car doesn’t have a spark plug and ignition coil.

Worn spark plugs or wires

Occasionally, spark plugs may outlive their service life and fail, resulting in a misfire. A damaged wire or cables may also trigger this on cars equipped with spark plug wiring. As a result, you might notice the lit check engine light due to such damages.

Vacuum leak

Leaks in the vacuum system often result in multiple misfiring cylinders or lean operating conditions. Additionally, they might be quite challenging to diagnose. This issue is more than enough to activate your car’s check engine light.

Defective fuel injector

A misfire occurs when a fuel injector does not deliver the correct quantity of fuel to a cylinder. Changing an ignition coil with a neighboring coil may be a straightforward task,while relocating a fuel injector is quite challenging.

Bad engine compression

Worse, a misfire causing your check engine light might also be caused by a burned or warped valve, damaged piston rings, or incorrect valve timing. These flaws can become evident throughout a compression test of the car’s engine.

Steady Vs. Flashing Check Engine Light

Whenever your check engine warning light is blinking or flashing, it often signals a misfire and other significant problems that need immediate attention and should be addressed promptly to the nearest auto repair facility. Overlooking a flashing light raises the likelihood of developing other issues, such as breaking a costly catalytic converter that could cost over $1,000 to repair certain vehicles.

Before going to the technician when the check engine warning light is on but not flashing, it is recommended to tighten the gas cap first since a loose gas cap might activate a check engine warning light. Check to see if the light turns out after a few restarts the next hour, day, or so. Replacing a worn-out fuel cap that doesn’t seal the tank completely might help resolve the issue.

What To Do If The Check Engine Light Is On

You will not completely understand whatever the check engine warning light indicates unless your vehicle is brought to a repair shop or diagnosed by a specialist. The warning might be for something minor and benign – or for something more severe that might result in further damage to your car.

When the engine warning light illuminates, you might need to tighten the fuel cap. Bear in mind that a check engine light might illuminate due to a loose fuel cap, so properly tightening the cap may resolve the issue. If the light goes out, there is no need to repair your vehicle. If the indicator remains on or flashing, it may signify a more substantial issue with your car.

You must avoid taking any risks. If the check engine light is on, get a professional immediately to diagnose and fix the problem.


Although there are several causes for your check engine light to illuminate, it’s important to remember that when the light is flashing, it signals that the engine is experiencing a severe problem that must be treated quickly. If the light continues to glow steadily, it signals a less severe issue but still must be brought in for diagnostics and servicing.

In any case, responding to the warning light right away will help avoid further harm to your automobile. Even if the car seems to be working flawlessly, you should get it thoroughly inspected to rule out whatever hidden issues that might result in expensive fixes if not addressed soon.


Is it safe to drive with the check engine light on?

Yes, you may drive for a short period with your check engine light on. Occasionally, the problem is as straightforward as a loose fuel cap. But sometimes, it might be more serious. However, it is recommended that you take your car for an inspection by a qualified specialist.

How do the technicians know the problem?

A technician will make use of a scanner or code reader gadget. They’ll connect the code reader to the car and do diagnostics. When the computer has decoded the code, the technician would determine the precise location of the problem and resolve it.

Why is my check engine light flashing?

A flashing check engine light implies a critical alert. This means that a fault with your catalytic converter might be occurring, which might result in overheating. If the check engine light is flickering, you should immediately bring your car for servicing.

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