Why Is My Check Engine Light On?

Why Is My Check Engine Light On?

As a car owner, a blinking check engine light may be problematic. Why is my check engine light on? – you wonder. But before you activate a panic mood, it’s safe to say not all engine lights will require an unwanted trip to the mechanic.

There are several reasons your check engine lights may come on, depending on the severity of the malfunction. It could be a loose gas cap, a failing catalytic converter, an oxygen sensor, a misfiring engine, etc. Whichever trigger is causing a flashing check engine light, it’s important to check and fix it.

Knowing check engine light indicators is one thing; finding ways to fix such is another. If you are wondering, “why is my check engine light on?” this article will walk you through possible causes and how to fix them.

why is my check engine light on - comparewise

What are check engine lights?

A check engine light, also known as Malfunction Indicator Lamp (MIL) or the “service engine soon light,” are lights that indicate a malfunction in a computerized engine-management system.

These lights tell you something is wrong somewhere and needs your attention. Check engine light indicators vary — ranging from a loose gas cap to a serious engine malfunction.

The check engine light is found in the dashboard of most automobiles, and depending on the manufacturer, it can be represented as ENGINE, SERVICE ENGINE SOON, CHECK ENGINE, EMMISS MAINT, MAINTENANCE REQUIRED, or a blinking engine icon.

When the car’s check engine light flashes, the computer indicates there’s a malfunction. The engine control unit generates and stores codes representing each malfunction. These codes can be read and interpreted using simple code readers.

Jul 30 - comparewise car loan banner

History of engine lights

Before the 1980s, automobiles had single indicators labeled as “Engine” or “Trouble”; they were also known as tell-tales or idiot lights.

They were less advanced than the Malfunction Indicator Lamp (MIL). This single indicator was in binary (on/off) and responsible for various faults, including overheating, low oil pressure, charging problems, and a possible engine knock.

The problem with these “engine” lights is no prior warning. The check engine lights come on after the malfunction must have occurred. Malfunctions cannot be detected or corrected earlier, making such vehicles expensive to maintain.

All thanks to technological advancements, the Malfunction Indicator Lamp (MIL) came into existence in the 1980s with computerized engine controls. Many models of automobiles from the early 1990s to 2000s have MIL based on the odometer readings.

Depending on the manufacturer, the check engine light can come on due to oxygen sensor failure; like in a Volvo car, this signal is represented as “lambda.” It may also come on after 130,000km in a Mazda model, which doesn’t signify a fault. So no code will be generated, and you will see a flashing check engine light for some time.

check engine light flashing - comparewise

False check engine lights

The car check engine light may come on if you start without giving your engine enough cranking time. This fault is common for most models. If you notice this, don’t sweat it. It may be a false engine light. All you need to do is restart your car and give it enough cranking time before turning the ignition ON.

You may also notice the check engine light near you comes on before starting your car. This light indicates that the lamp still works and should come off immediately if no malfunction is noticed.

Types of engine lights

Your engine light is on — what next? Once the MIL comes on, it’s an indicator of a malfunction. This light flashes in two stages depending on the severity of your car’s fault. They are as follows:

  • Solid Light:  The solid check engine light is an indication of minor faults which are not emergencies. However, it would be best if you didn’t ignore it. Instead, get it checked out to avoid escalation.
  • Flashing Light: The flashing engine light indicates a major malfunction, often a severe engine misfire. This malfunction causes unburned fuel to get into the exhaust system and can increase the catalytic converter’s temperature, thereby causing damage or a fire hazard if left unchecked.

It is important to note that today’s automotive computers try to compensate when there is a malfunction. But, unfortunately, you may not realize your car’s functionality declined until it’s too late.

Possible reasons why you see flashing check engine lights

Several reasons can result in your check engine light turning on. Below is a list of common reasons for check engine light:

Gas cap

The gas cap, also known as the fuel filler cap, is an important part of any automobile. It’s responsible for the following:

  • Maintaining the pressure of the fuel delivery system.
  • Sealing the fuel tank to prevent leakage.
  • Preventing dust and dirt from getting into the fuel tank.
  • It helps capture and reuse fuel vapour.

The fuel filler cap is a frequently used part of your car. It is opened and closed as many times as your car needs refilling. This piece of equipment is designed to click after tightening. However, it may wear out from continuous usage.

If your gas cap keeps popping after sealing it, that’s a sign it needs replacement. It is relatively inexpensive to change a gas cap; a universal-fit gas cap costs about $15 at any automobile parts store.

A loose gas cap is the most common trigger for flashing check engine lights. But, aside from the engine lights, there are other signs your gas cap may have malfunctioned. For example, you may perceive fuel in your car, or your vehicle starts to jerk, making it less efficient.

Once your hunch is telling you your gas cap may have malfunctioned, it’s good to stop by a safe spot and get it checked out. Most likely, you just left a gas station, and the cap wasn’t properly sealed or left uncovered — Being in a hurry is no man’s fault; we all have those busy days.

If, after sealing off the gas cap, you are still perceiving the smell of fuel, and the car check engine light stays on for more than a day, Your car may need a fuel system inspection, and you should consider visiting the nearest maintenance shop.

check engine light is on - comparewise

Catalytic converter

This expensive metal is found in your car’s emission system. It is responsible for converting pollutant gases from the exhaust into less damaging ones. For example, a faulty catalytic converter triggers a flashing check engine light.

A malfunction as major as this will be expensive to fix. Approximately $945 to $2475 is needed, including labor and the cost of parts. Although catalytic converters last for 10 years and above, they hardly need replacement except when broken or necessary.

Because maintenance is expensive, it’s important not to ignore the red flags. Here are signs of a damaged or failing catalytic converter:

  • Dark smoke from the exhaust
  • Rotten egg smell in the exhaust
  • Slow performance
  • Failed emissions test

A new catalytic converter costs between $200 and $600. The good thing is that repair is avoidable only if you are consistent with your car’s maintenance checklist. Therefore, it would be best if you considered following this routine:

  • Check often for dark smoke from the exhaust.
  • If you only drive your car to the office or the grocery store, you may consider taking your vehicle on a long drive to avoid clogging the catalytic converter.
  • Change the oil frequently. Old engine oil gets dirty and runs through the engines, affecting the catalytic converter.

Oxygen sensor

An oxygen sensor is part of your car’s emission system that helps regulate the amount of air and gasoline in the engine. It works hand in hand with the catalytic converter. If this sensor is clogged with ash, it can decrease the gas mileage and increase emissions.

A failing oxygen sensor will trigger a flashing check engine light. Although oxygen sensors don’t cost a fortune to fix, unlike catalytic converters, a frequent check will save you money. A new O2 sensor will drain your savings of $175. I’m sure that’s not an expense you want on your list.

New model cars have more than one oxygen sensor. If you are wondering how many sensors your car has, here is a quick trick:

  • Check to see how many exhaust pipes your car has.
  • One exhaust pipe has one catalytic converter.
  • Each catalytic converter has two oxygen sensors.

Aside from a flashing check light, here are other signs your oxygen sensor is malfunctioning:

  • More trips to the gas station as you are burning fuel more than expected.
  • High emissions
  • Rotten egg smell from the exhaust
  • Dark smoke from the exhaust
  • Slow engine performance
  • Failing emissions test

Detecting these warning signs early will save you money because a failing oxygen sensor is equivalent to a failing catalytic converter. If you notice any of these signs, an experienced vehicle mechanic will be required to repair it.

Mass airflow fensor

The mass airflow sensor regulates the amount of air passing through the engine and keeps it running smoothly. This piece of metal is part of the engine management system of your car and has no expiry date. It can stay useful for a long time; a replacement is highly unlikely. Although they sometimes malfunction.

If you are on a highway and finding problems with accelerating, your mass airflow sensor might have malfunctioned. A failing mass Airflow sensor will give off the following signs:

  • Flashings check engine light
  • Difficulty starting the engine
  • Jerking engine
  • Slow response to acceleration.
  • Dark smoke from the exhaust
  • Rough idle

If your vehicle shows signs of a faulty mass airflow sensor, consider replacing the air filter or cleaning the sensor with a mass airflow sensor cleaner. If the problems worsen, your vehicle may malfunction due to other issues. Have it checked out.

Spark plugs and wires

Spark plugs and wires are essential components of your engines. They are in charge of sending current from the ignition coil to the plugs. These plugs convert low-voltage to high-voltage energy, allowing you to start your engines.

Spark plugs and wires in good working order will benefit you by reducing pollution, increasing fuel efficiency, and making your car run more smoothly. A sudden drop in your car’s gas mileage is an indicator of faulty spark plugs and wires, which can trigger a flashing check engine light.

The spark plugs and ignition wiring goes hand in hand. Therefore, it is advisable to change both when one is faulty for optimum performance. Also, spark plugs only apply to automobiles that run on gasoline, as those with diesel use glow plugs instead.

Vacuum leak

A vacuum leak is anywhere between the engine and the mass Airflow sensor. This leak will impair the functionality of the mass airflow sensor, which regulates air intake, making the engine run lean, a situation where the air intake is higher than the fuel intake.

If your engine begins to hiss, struggles to maintain stability, or stalls when stopping with a flashing check engine light. It’s a sign of a possible leak. Common sources of vacuum leaks include:

  • Cracked intake boot
  • Leaking intake manifold gasket
  • Cracked vacuum hose
  • A stuck-open EGR (Exhaust Gas Recirculation) valve
  • An installed brake booster

Why is my check engine light on conclusion

So, once your car’s check engine light flashes as a result of any of the above, whether minor or major, I recommend you find a safe spot and switch off your engines. Then have your vehicle checked for possible malfunctions. But, again, it’s better to err on the side of caution than to be found wanting.

You might also like…

Discover Investment Opportunities

Make your money do more.

12 Results

Advertiser disclosure

Offers shown here are from third-party advertisers. We are not an agent, representative, or broker of any advertiser, and we don’t endorse or recommend any particular offer. Information is provided by the advertiser and is shown without any representation or warranty from us as to its accuracy or applicability. Each offer is subject to the advertiser’s review, approval, and terms. We receive compensation from companies whose offers are shown here, and that may impact how and where offers appear (and in what order). We don’t include all products or offers out there, but we hope what you see will give you some great options.

Young investors can trade stocks and ETFs, all for free.
Min Investment
Target Return
Get up to $2,200 in welcome rewards
Min Investment
Target Return
Invest in a 3.25% 5-year GIC today.
Min Investment
Target Return
Flexibility with a great return.
Min Investment
Target Return
Get up to $150 cash bonus
Min Investment
Target Return
High return on a shorter term.
Min Investment
Target Return
Sign up & Get $20 in BTC
Min Investment
Target Return
Buying and securing gold has never beeng more simple and affordable.
Min Investment
Target Return
Buy and sell gold, silver & platinum online at the best price.
Min Investment
Target Return
Retire up to 30% wealthier with Questwealth Portfolio.
Min Investment
Target Return
Get a $100 welcome bonus, when you make your top-up*
Min Investment
Target Return
Get $25 bonus with code: 9APOU9
Min Investment
Target Return

FAQs about why is my check engine light on?

What should you do if your check engine light is on?

When you see a flashing check engine light, look for other symptoms to help narrow down the problem. If no symptoms are obvious, you can perform an overall maintenance checklist. This includes tightening the gas cap, checking the oil level and replacing it if low, cleaning the air filter, and other tasks.

How do I turn off my check engine light?

If your check engine light comes on, an error code will be generated representing the malfunction. To decipher the codes, do-it-yourselfers can use an inexpensive code reader. Once you have this equipment, you can read the codes, google them, and look for possible solutions. Then, for a fee, hire a mechanic to inspect and repair the problem.

Is it safe to drive while the check engine light is on?

Driving with the engine lights on is safe for a minor fault. The lights will be steady rather than flashing if it is a minor fault. Flashing check engine light is an indication of a major fault, and it's not safe to drive.

Why is my car’s check engine light on?

There are several reasons why your check engine light may come on—ranging from a loose gas cap, a possible leak, or a failing catalytic converter or oxygen sensor to a dead battery.

What does the check engine light indicate?

Check engine lights are warning lights signifying a possible malfunction in your vehicle. Depending on the manufacturer, these lights may come in amber, yellow, or red.


November 7, 2022
Fact Checked

Grow your finances today.

By submitting, you agree to comparewise’s terms of use and privacy policy.

You may also like

The Vehicle Identification Number (VIN) is a unique code assigned to every vehicle. Thi...
With the increased awareness of environmental pollution from greenhouse gasses, more dr...
Are you in search of the best small cars in Canada? Urban area living becomes challengi...
Finding and deciding on the best used SUV in Canada is much easier said than done. This...
If you’ve considered buying the new Tesla cybertruck, we can’t blame you. It looks so f...
Car loan?
Personal Loan?

Top deals await you just a short
application away!