Check Engine Light

Check Engine Light Blinking- The Complete Guide For Car Owner

Mike Cross
Updated Feb 13, 2022
Check-Engine-Light-The-Complete Guide-For-Car-Owner

You’re driving like any usual day. And suddenly it happens. The Check Engine Light pops on. What could be the problem? How serious is it? There are plenty of common problems that could be going on with your vehicle that could trigger a check engine light to come on.

In fact, there are ten common reasons that we’ll be looking at. We’ll be taking a look at what may cause the specific issue, how serious it can get, and whether or not you can solve it yourself or by way of a professional mechanic.


What Does Your Check Engine Light Mean?

When your check engine light (or “service engine soon”) comes on, it means that there may be one or more problem codes that will be stored inside of your vehicle’s computer. Even if the light doesn’t come on, there’s a good chance that the diagnostic codes will still be stored on the computer itself. Also, the check engine light may flash solidly or flicker. This may depend on the severity of the issue. Even the most minor issues can trigger the light to come on. It could also be a good indicator to let you know that it’s time for its annual checkup.

You should also keep in mind that the check engine light can also be illuminated in different colors. This will depend on the manufacturer of your vehicle. The light can be solid or blinking. Also, the color of the check engine light will depend on the severity of the issue. Your vehicle’s manual may have a color code for your check engine light to help you determine the severity of the problem.

10 Common Reasons That Cause The Check Engine Light To Come On

1. Bad Spark Plugs

Symptoms Of Bad Spark Plugs
Bad Spark Plugs Can Cause Check Engine Light

What causes it:

Usual wear and tear, a buildup of carbon and debris, age

How serious is it:

A bad spark plug is serious as it can harm the fuel economy, make idling and starting your vehicle rough, and cause further damage to the engine.

What to do:

Replacing it would be the best course of action. A great quality spark plug will last you nearly $20 to $25 at best. In fact, you should consider changing the spark plugs every 100,000 miles instead of waiting until the first sign of trouble. These can be found either online or at your local auto parts store.

Why are they important:

The spark plugs are used to produce the spark that ignites the air and fuel mixture. This will help your engine produce power. The spark plugs create electrical arcs without touching each other (but will be close enough so electricity can be able to make it through the gap between them.)

The spark plugs are a key component to your vehicle’s ignition system. A great quality spark plug will sustain multiple amounts of electrical explosions that will occur when you are starting your vehicle and while you are on the road.

However, there will come a time that your spark plugs will wear down and become susceptible to corrosion. As corrosion worsens, it will wear down the spark plugs considerably and will lead to electrical arcs that will weaken or get smaller.

When not taken care of properly, there will be instances where you will have a hard time starting your vehicle. Also, once you can replace your spark plugs you should make a note of your odometer. This way, you can keep track of miles you rack up over time. As mentioned, it is highly recommended that you replace your spark plugs every 100,000 miles or thereabouts.

2. Bad Oxygen Sensor

What causes it:

The buildup of ash, debris, fuel additives, wear and tear

How serious is it:

A bad oxygen sensor leads to increased emissions and your vehicle will burn through more fuel than normal. In other words, you may go through a tank of gas fairly quickly.

What to do:

A bad oxygen sensor cannot be repaired. Replacing it will be your only option. Most new oxygen sensors will likely be somewhere within the $200 to $250 range.

Why is it important:

Your oxygen sensor is a key component to your vehicle’s exhaust system. It will work with your vehicle’s computer to relay the information regarding the emission levels in order to optimize performance. It’s important for your vehicle to find a fuel-to-oxygen ration that will be optimal for your vehicle. This is a critical component that you want to make sure that its in working order.

Any sign of failure may spell trouble for your vehicle. You’ll know it when your emissions are all of a sudden increase to dangerous levels. It is important for your mechanic to check on the condition of the oxygen sensor if and when your vehicle is undergoing its regular check-up and maintenance. That way, you can be able to stay on top of any issues at the earliest sign possible.

One thing you need to realize that unlike some parts that need to be changed on a routine basis, an oxygen sensor does not have a limit as far as mileage goes. In other words, you won’t need to change it every 50,000 miles or so. But that doesn’t mean you should forego checking on it from time to time. Also, some users have reported oxygen sensor failure even without the check engine light coming on. That may also mean having to monitor for any symptoms if and when they occur.

3. Loose Gas Cap

What causes it:

You forgot to put it on or there’s a large enough crack on the cap itself.

How serious is it:

It’s pretty serious if there are gas vapors leaking out of it (not to mention, a recipe for disaster). Your fuel system may also get thrown off course as well.

What to do:

Double-check to see if the gas cap is tightened after you’ve fueled up. If the gas cap is cracked, replace it. It should cost you no more than $15.

Why is it important:

A gas cap will minimalize the amount of evaporation that can and will occur in your gas tank. Not to mention, a gas cap is designed to protect the entire fuel system from any dirt or debris that might be able to gain access and cause a lot of damage. With dirt and debris damaging your fuel line, that will cause the fuel economy to suffer in the process.

While it’s not necessarily dangerous to drive without a gas cap, it’s not the smartest thing to do. That’s because you’ll be asking for more vehicle trouble if you are driving without a gas cap in the long-term. Even though there is a flap that seals off the gas tank, it still may not be enough to cause some kind of ignition from happening based on external environmental factors (i.e.-- a close-range spark or a cigarette burning near the gas tank).

If you have no gas cap, it would be better to get one now rather than put it off. Fuel line problems will lead to even bigger problems. And if those problems are left unchecked, you might find yourself without a vehicle and a very hefty repair bill. What may seem like “not such a big deal” will eventually become one if nothing is done.

4. Failing Catalytic Converter

What causes it:

Bad spark plug or oxygen sensor

How serious is it:

This includes two of the previous common causes we’ve already covered. This is at this point one of the most serious issues that will cause bad emissions and wasted fuel.

What to do:

Unless you are a professional mechanic yourself, replacing the converter won’t be easy. Expect costs to be roughly $1000 to $1200 at the most.

Why is it important:

It’s true that a car’s emissions can cause pollution. However, if it weren’t for a catalytic converter, cars would be much more of a threat to the environment now more than ever. One of the main things that a vehicle’s exhaust system produces is carbon dioxide. It also mixes with other harmful pollutants due to the unstable amount of the fuel to air ratio. Aside from carbon dioxide, it also produces carbon monoxide, hydrocarbons, and nitrogen oxides. The catalytic converter will catalyze these chemical reactions in the air and turns them into less harmful chemicals.

The way the catalytic converter works is done in two phases. In the first phase, the converter will remove the nitrogen oxides by breaking down the nitrogen atoms from the nitrogen oxides. Then nitrogen and oxygen gases are created from that process. In the second phase, the converter does the same thing only this time with the carbon monoxide and the hydrocarbons. These are then oxidized and soon converted into carbon dioxide. Carbon dioxide is not really harmful to the environment. But it is important to make sure that even today’s vehicles do a better job of polluting less and be able to provide a reliable transportation option for those who drive from point A to point B on a daily basis.

5. Bad Mass Air Flow Sensor

What causes it:

Improper installation or neglecting to replace it.

How serious is it:

A number of problems can go wrong for your vehicle. This will include stalling, increased fuel emissions, poor engine efficiency, etc.

What to do:

A mass airflow sensor should be replaced on an annual basis. You can be able to easily replace it for just $380.

Why is it important:

The mass airflow sensor is yet another critical component of your vehicle that you should never neglect at the first sign of trouble. It measures the air mass (NOT the volume) of air passing through the intake. It will then relay that information to your vehicle’s computer system. A mass air flow sensor will be found in vehicles that use fuel injection as opposed to carburettors.

Keep in mind that the air flow will change depending on the temperature, the altitude, and forced induction (if it’s being used). It’s important to have a mass air flow sensor that will be able to accurately read the air density and make adjustments if needed. At the same time, it will also relay these changes to the computer.

There are three types of mass air flow sensors:

  • Moving vane
  • Hot wire
  • Cold wire.

A moving vane MAF will be present in most older vehicles with fuel injection. These sensors will have small vane or flap that will push open to allow air to flow through.

Hot wire sensors will be found in your more newer vehicles. These sensors will heat up and will cool down when the air flow passes through.

Cold wires are similar to hotwire sensors. The only difference is that it adds an additional wire that is designed to read baseline stats for your vehicle.

6. Bad Ignition Coil

Bad Ignition Coil Symptoms
Bad Ignition Coil

What causes it:

High temperatures, wear and tear

How serious is it:

If your ignition coil has gone bad, there’s a good chance that you’ll be having engine trouble at some point down the road.

What to do:

Replace it immediately, if possible. It’s easy to do it yourself and will only cost you $200 to do so.

Why is it important:

The ignition coil works in conjunction with your car’s computer and also your spark plugs. It is the ignition coil’s responsibility to help deliver the power to the spark plugs so they can be able to produce the electrical arcs to complete the ignition process. Some cars will have one coil that will deliver enough power to two spark plugs.

However, if your vehicle has a six cylinder engine, you’ll likely have an upwards of six coils. It is so important that this ignition coil should be in working order. Because if it doesn’t, it will also cause your spark plugs to fail as well.

Once again, an ignition coil is not one of those parts that has to be changed every hundred thousand miles or thereabouts. But it’s always a good idea to get it looked at if and when your vehicle is undergoing its annual maintenance. It shouldn’t be stressed enough that early detection of something that can (and will lead to further vehicle issues) can be prevented if and when you catch it. Don’t wait for the check engine light to come on or wait for symptoms that might be in the advanced stages of failure.

7. Bad thermostat

What causes it:

You may be exposing the thermostat to a bad environment. It may be enough to damage the thermostat due to corrosion, debris buildup, etc.

How serious is it:

A bad thermostat will give you misreading. When a thermostat goes bad, the engine faces a high risk of overheating.

What to do:

This is another issue that a mechanic will be able to solve. The repair cost shouldn’t be ridiculous. About $200 to $250 will be what you might be paying for replacement and labor costs.

Why is it important:

No one wants to deal with an engine that will heat up fairly quickly. Because if the engine gets too hot, it will fail and may also render your vehicle useless. Like your thermostat at home, your vehicle also has a thermostat that will maintain an ideal temperature for your vehicle. That temperature should be enough to run the vehicle with efficiency. Your thermostat serves as a valve between your vehicle’s engine and the radiator.

Your thermostat will be closed when you start your vehicle and will allow the coolant to warm up to that optimal temperature. Once the coolant reaches that temperature point, that’s when the thermostat valve opens. This will allow the coolant to flow to ensure that the temperature is maintained at that level. The valve will repeatedly open and close so it prevents the engine from overheating.

While it might trigger the check engine light if there are temperature issues, that’s not the only warning light that you will need to focus on. It will also trigger the “check temperature light”. Also, your thermostat might be to blame if you are unable to get hot air to blow through your heating system during the winter time. If such a thing occurs, then you might want to check on your thermostat and your heating and cooling system as well.

8. Aftermarket Car Alarm Is Non-Compatible

What causes it:

Improper installation or not compatible with your vehicle at all.

How serious is it:

As crazy as it sounds, a non-compatible car alarm can be harmful to some of the other systems in your vehicle.

What to do:

See if you can properly reinstall the system. Follow the instructions in the owner’s manual. Alternatively, you can get it replaced completely for just $100.

Why is it important:

Obviously, a car alarm is intended to deter any car theft or burglaries from occurring. But what sets an aftermarket car alarm apart from the others? It is said that an aftermarket car alarm will produce a much louder noise. The louder it gets, the better the chance a would-be car thief or burglar will flee considering that it will be loud enough to draw the attention of people in the surrounding area. On top of its ability to be loud, an aftermarket car alarm will have several different features compared to an OEM car alarm. Plus, aftermarket car alarms will mostly be more “beefier” in terms of security than it’s OEM counterpart.

For example, aftermarket car alarms will have an LED light indicator that will let you know that your vehicle’s alarm system is armed or disarmed.

Aftermarket alarms will also have shock sensors that will pick up on any incidents of shock and impact. It can even trigger if your vehicle is being moved or towed. As a random note, if you ever were to hear a car alarm go off in the middle of a public parking lot, chances are that it’s a vehicle that’s equipped with an aftermarket alarm. It could be due to its sensitivity to shock and impact. Even the slightest bit of contact may set it off if it’s turned on.

9. Leaky Vacuum Hose

What causes it:

Bad vacuum lines or a bad gasket.

How serious is it:

This will lead to a lot of issues ranging from poor fuel efficiency to increased emissions.

What to do:

Replace the hose(s). They can be easily installed and won’t cost you anywhere north of $100.

Why is it important:

Every single vehicle has these vacuum tubes. This is another critical part of your vehicle you don’t want to ignore if it’s having problems. This vacuum tube or line is connected to the vehicle’s manifold vacuum. In fact, there are at least a dozen of these connected throughout your vehicle so it can allow some parts to function properly like your windshield wiper motor, the vacuum brake booster, and more. Vacuum hoses come in different measurements. The smallest hose will be measured at 1/16” while the largest is measured at ⅜”. The size you need will depend on the vehicle. These tubes are mostly made from rubber, but the higher quality vacuum tubes will also include other materials like silicone. The latter will be much more useful if the vacuum tubes are frequently exposed to heat. The silicone will keep the tubes cool and prevent any damage due to overheating. Since the vacuum tubes are made from rubber, they will wear down over time. It would be a good idea for you to have them checked for any signs of wear during your annual checkup. That way, they can replaced if needed. The sooner you can change them out, the better.

10. Bad Gas Recirculation Valve

What causes it:

Frequent opening and closing.

How serious is it:

A bad valve will spell trouble for your engine. You will have a very difficult time starting it. Plus, there will be constant episodes of stalling.

What to do:

You can be able to replace the part and install it yourself. A new gas recirculation valve won’t cost you any more than $350.

Why is it important:

The gas recirculation valve is responsible for preventing pollution. In this case, unburned fuel will be released into the atmosphere if it weren’t for this most important part of your vehicle. One of the main culprits to the increase in greenhouse gas emissions is believed to be unburned fuel produced from vehicles. Like any other valve in your vehicle, it’s supposed to repeatedly open and close so it prevents any unburned gas from escaping. It also has a responsibility to reduce nitrogen oxide emissions in your exhaust system. If your vehicle is undergoing a partial load, this valve will also play a role in reducing gas consumption in this specific situation.

There are two kinds of gas recirculation valves: pneumatic and electrical. The latter can be found in most newer vehicles. Pneumatic valves are controlled by what is known as a poppet valve. Electrical valves have a poppet valve and also additional valves that will give the entire gas recirculation system better control and short adjustment times to boot. In fact, the electrical types have a more complex setup compared to its pneumatic counterpart. This means that it will have a better chance of dealing with unburned fuel.

How To Reset The Check Engine Light?

Check-Engine-Light-The-Complete Guide-For-Car-Owner
Check Engine Light-The Complete Guide For Car Owner

There are two ways to reset the check engine light. First, you can use an OBD scanner. You can also do this without the use of one. Let’s take a look first at the OBD scanner option:

1. Using an OBD scanner

If you don’t have an OBD scanner, you’ll need to purchase one as soon as possible. In fact, you should have one period just in case your check engine light ever does come on. Depending on the device’s functionality, an OBD scanner could range anywhere between $20 to $1000 in price.

Today, vehicles dates from 1996 to today will need an OBD II scanner. If you have a vehicle that is made from 1995 or before, you’ll need a regular OBD scanner. There are two types of OBD II scanners on the market. Here’s what they are:

Code readers:

This OBD 2 scanner will be an inexpensive scanner. It’s purpose is to read and clear any problem codes from your vehicle’s computer. While it is affordable, it’s one downfall is that it may not have codes that are unique to certain manufacturers. Because of this, these scanners may not access the data that is associated with those codes.

Scan tools:

Of course, scan tools will be your more expensive option. The only major difference it has of course is the ability of tasks that code readers do not have. It can read manufacturer specific codes, provide advanced troubleshooting options, and provides access to live and past recorded data.

When should you purchase either?

This will depend on how much money you are willing to spend. However, if you are more technically inclined, an OBD scan tool will be your best bet. If you want something simple and affordable, a code reader will do. It will be able to give you the same codes that are stored on your vehicle’s computer. Once you retrieve the codes, that’s when you’ll look them up for yourself by way of your owner’s manual or online. You can read more on my article to compare scan tool vs code readers here

Resetting The Check Engine Light With an OBD Scanner

Resetting The Check Engine Light With an OBD Scanner
Resetting The Check Engine Light With an OBD Scanner

1. Connect the scanner to your vehicle and look for codes

Your car should have a port for connecting the OBD scanner or using bluetooth car diagnostic tool. Most of the time, this should be located on the driver’s side of your dashboard. Find the bluetooth scan in this link.

Before you connect the scanner to the port, be sure that your vehicle is shut off. Once connected, turn the key to the “on” position (but don’t start the vehicle entirely). Press the “scan” button when ready.

2. Look up your codes

There are two ways you can look up the diagnostic codes or DTCs. First, your vehicle might have a built-in library letting you know which codes represent a certain issue. Alternatively, your owner’s manual might have this. You can also look for the codes online.

3. Replace the affected part

This is self-explanatory. You can replace the part that is affected fairly easily (unless otherwise instructed). You can get the part through an auto parts store or online.

4. Erase the code if and when necessary

If you clear the codes from the OBD scanner, they may disappear temporarily. After your press the erase or clear button from your scanner tool, wait to see if there are no more codes. If you are clear, you can shut off the vehicle and disconnect the scanner. Keep in mind that just because the codes are erased, doesn’t mean that the problem is solved. If the check engine light pops back on, you may need to take it to a professional mechanic to figure out what is going on. This could also mean that you might be also dealing with an underlying problem that you may not be aware of.

What To Do When You Get A Code Using The OBD Scanner During Reset

Of course, if you get a code while resetting your check engine light it’s important to determine which code it is. The check engine light may come on even if you have replaced what you believe is the “problem part”. On the safe side, you may want to take it to a mechanic just in case you might have missed something that should have been addressed while ago. Otherwise, if nothing wrong is detected by your mechanic, you can simply clear the code from the computer.

Resetting Without an OBD Scanner

Is it a good idea to do this?

While some people will do this method, others are actually opposed to the idea. That’s because it would be hard to tell if and when the OBD codes are still in place on the vehicle’s computer. Plus, you also risk having to deal with any other underlying problems that will still trigger the “check engine” light. If this is the case, then obviously taking it to a professional mechanic is your only solution. If you choose to use this method, do so at your own risk.

How To Reset check engine light without an OBD Scanner step by step

Park your vehicle safely

No explanation needed. This could be in your driveway or garage.

Remove the battery cables

Remove the negative (black) and the positive (red) cables from your battery. Make sure they are separate from each other so they don’t touch. However, disconnecting the battery can cause some parts of your vehicle to reset. This could include but not limited to your radio/stereo system or your vehicle’s built-in clock. If you have any preset stations, you may want to re-save them if the memory is cleared. Likewise, you’ll also need to re-set the manual clock to the correct time. You should regularly maintain your car battery, it will work correctly.

Ignition cycling

Cycle the ignition by repeatedly turning the car on and off for at least 3 to 5 times. This does not mean starting the vehicle completely.

Press the horn button

Press on the horn button for about 30 seconds. This will allow you to drain the ECU capacitor of any leftover power.

Wait 10 to 15 minutes

Prior to connecting the battery cables, wait 10 to 15 minutes.

Retighten the battery cables

Self-explanatory. Black goes negative, red goes positive.

Re-start the vehicle

Turn on the vehicle like you usually do and check for any lights. At that point, your check engine light should be shut off.

5 Common Codes You Can Get When Running an OBD Scanner

The following are the five most common codes you might get when you are running an OBD scanner. Use this as a guide if needed. If your code is not present on the list, consider using online resources to find the proper code. Here are five codes you need to know:


These codes are present when there are issues that are pertaining to your oxygen sensor.


Indicates an engine misfiring. This will likely be accommodated by any engine sputter, vibrations or shaking. This may be common in cases if you are dealing with bad spark plugs or the ignition coil.

P0411, P0440, P0442, P0442, P0446, and P0455

These are linked to your vehicle’s evaporative system. This is a common code that could also involve parts like your gas cap. If you have a missing or cracked gas cap, you may get one of these codes.


This code is unique to your gas recirculation system. If you are dealing with issues that include the valve, this code will likely pop up on your OBD scanner.

P0420 or P0430:

Associated with the catalytic converter. Depending on the issue ranging from age to leaks, either one of these codes will pop up on your scanner.

FAQ - Frequently Asked Questions About Check Engine Light

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

It depends. If the light is holding steady, you can still be able to drive safely. But at that point, you should monitor your vehicle and the way it behaves. The sooner you deal with the issue, the better off you’ll be.

How far can you drive with it?

Again, it will depend on the issue. You can be able to drive a vehicle for hundreds of miles. However, you may need to check your vehicle using an OBD reader so you can retrieve the proper code. Such codes indicating a faulty oxygen sensor or fuel valve is as serious as you can get (meaning you shouldn’t drive too far).

Will the check engine light reset itself?

Only if you have replaced the faulty part in question.

Can you trade in a car with a check engine light on?

It will depend on the dealer. Issues that trigger a check engine light may not be as serious. An in-house mechanic will make sure that any issue is addressed before the vehicle is re-sold.

Can I pass a smog test if my check engine light is on?

No. In fact, if your oxygen sensor is bad and the check engine light is off, you will still fail a smog test.


It’s important to take your check engine light seriously, even if it seems like a minor issue. Because ignoring it can yield some very negative results. It is highly recommended that you get an OBD scanner and keep it handy just in case your check engine light does come on. Early detection will definitely save you a lot of headaches and frustration in the future.

Mike Cross
Life is too short to drive with stock audio

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