Check Engine Light Comes On And Off – What’s Causing It?

Check Engine Light Comes On And Off – What’s Causing It?

Everyone knows that a check engine light usually means that something is terribly wrong with the vehicle. But, what about a problem where the check engine light comes on and off? This might even be a normal sight if you are driving a car that is more than 10 years old, or when a part passes a certain age or miles.

The most probable culprits for this issue usually are bad sensors, faulty spark plugs, or ignition coils. These things are not meant to last forever, and especially when the car is not driven regularly, they know to break and cause some headaches for car owners.

In this guide, we’ll be taking a closer look at all the main causes why a check engine light comes on and off. Moreover, for each of those causes, we’ll look more closely at the symptoms, diagnostics, troubleshooting, repair steps, and costs to fix each of them for good.

We’ll even take a quick look at how you can reset or fix the check engine light with some simple steps, and much more!

Check Engine Light

Check Engine Light Comes On And Off

Before we dive deep into this topic let’s discuss some basic things. For the people that saw their first check engine light and are still beginners when it comes to cars. This will help them learn about these things. If you are one of those people that still haven’t seen it, good for you because for some of us that is a basic routine.

The check engine light is a special indicator installed in your cluster. It has a function to turn on when there is something wrong with your power unit. This orange light usually appears and turns on when you put the ignition key along with other lights.

After you start the car it goes away immediately. But only if the car is in perfect shape and doesn’t have problems. If it does have a problem. This light is going to haunt you until you say it’s enough and decide to get rid of it and visit a mechanic.

Although when people see this light many of them presume that there is something really bad with the car and something seriously went off. But that doesn’t need to be the case. It can be something simple as a spark plug, or your gas cap may not be fully shut.

What Causes Check Engine Light To Come On

It is important to address this issue immediately. If you leave it on and pretend like you don’t see it something seriously may go wrong. You may be left stranded by the end of the road. And you will scratch your head about why you didn’t fix this sooner.

So, don’t be that guy and when you see this light, it needs to be checked quickly. Go to your local mechanic or do it DIY, something that we will discuss later in this article.

Since we explained more about the check engine light and its purpose now let’s dive deeper into the problematics. Let’s see what causes a check engine to come up in the first place. There are quite a few reasons and protentional culprits for this problem. Some of them are very serious and some of them are not that potentially dangerous for your engine’s overall health.

Check Engine Light Comes On And Off

First, let’s take aside the things that make the check engine light turn on and stay that way. This is a bigger issue than a flashing check engine light. These problems may cause severe engine damage if left untouched. Some of them are:

Check Engine Light Comes On, Potential Causes #1: Bad Ignition Coils

Bad ignition coils, coils are known to go bad especially if the car doesn’t run that often and is left unused. Bad coils may cause your engine to run rough and unbalanced because there is not enough spark to burn the fuel. When the engine is misfiring, you can notice right away if it runs unevenly.

The solution to this problem is a new ignition coil. They are not very expensive and you can do it by yourself at your home. But if you want to save yourself from future headaches it’s best to change all of the coils in your car. This can come up to a big price but the car would run perfectly for a long time.

Symptoms of Failing Ignition Coils

If the ignition coils of your car are failing, there are several signs you can look out for. Firstly, your car might be hard to start or it might not start at all. This happens because a bad ignition coil can affect the timing of the engine’s spark, causing starting difficulties.

Secondly, you might notice your car’s engine misfiring or running roughly. This happens because a failing coil may not provide enough spark for the fuel to ignite properly. Misfiring can also cause reduced fuel economy, and you might notice your car is burning more fuel than usual.

Finally, a car with a bad ignition coil might also exhibit a lack of power and stalling, especially when the engine is under stress, such as during acceleration or uphill driving.

Diagnosing Bad Ignition Coils

The symptoms of a bad ignition coil can also indicate other problems, so it’s important to perform a proper diagnosis. A common method for testing ignition coils is using an ohmmeter or a multimeter to measure the resistance of the coils.

Each coil should have a specified resistance value, which you can find in the vehicle’s repair manual. If the resistance is too high or too low, this indicates a problem with the coil. Another method of testing is using a spark tester. This device can tell you if the coil is producing the necessary spark to ignite the fuel in the engine.

Fixing Bad Ignition Coils

To fix a bad ignition coil, the coil will need to be replaced. If you have some experience working on cars, this is a job you can do yourself. The process generally involves disconnecting the battery, removing the old coil, installing the new coil, and reconnecting the battery.

However, it’s important to follow the specific instructions in your car’s repair manual to avoid causing further damage. If you’re not comfortable doing this job yourself, it’s recommended to hire a professional.

Costs of Replacing Ignition Coils

The cost of replacing ignition coils can vary widely depending on the make and model of your car, and whether you choose to do the job yourself or hire a professional. Generally, you can expect to pay between $70 and $350 for a new ignition coil. If you hire a professional, labor costs will add to this price.

Remember, if one coil is failing, it might be a good idea to replace all the coils at once. Although this increases the upfront cost, it can save you time and trouble in the future.

Check Engine Light Comes On, Potential Causes #2: Malfunctioning Fuel Injectors

Bad fuel injectors, injectors can also go bad and these can cause some big issues when they are broken and your engine may run rough or don’t run at all. They are a crucial part of the ignition system.

Because if you do not have injectors that pump in fuel in the cylinders at the right PSI of pressure, the car will not run as it used to and you may lose power and it can leave you stranded. So, if this is the issue a new injector will be the solution.

Injectors come at high prices, especially if you drive a diesel car or truck. They can cost a few hundred dollars and more, mostly because they are a piece of high-precision machinery. But there are also a ton of companies that repair these injectors for a fraction of that price and you can go with that option.

Symptoms of Failing Fuel Injectors

When the fuel injectors start malfunctioning, it doesn’t take long for signs of trouble to appear. One of the most noticeable symptoms is a rough idle. If the fuel injector doesn’t spray enough fuel into the engine, the car can’t maintain a steady idle speed and starts to run roughly.

The second symptom you might encounter is decreased fuel efficiency. If your car starts consuming more fuel than usual without any significant change in your driving habits, it might be due to a malfunctioning fuel injector.

Lastly, if you experience difficulties in starting your car or if your car’s engine stumbles and misfires during acceleration, a bad fuel injector might be the culprit. Such issues often stem from an imbalance in the air-fuel mixture due to the injector’s failure to supply the correct amount of fuel.

Diagnosing Malfunctioning Fuel Injectors

Diagnosing a bad fuel injector involves a series of steps. A common method is to use a mechanic’s stethoscope or a long screwdriver to listen for a clicking sound which indicates that the injectors are functioning. No sound may mean a malfunctioning injector.

Another method is to use a digital multimeter to check the resistance of each injector. The resistance should be within the range specified in your car’s manual. Too high or too low resistance can indicate a problem.

Lastly, you can visually inspect the injectors. Any leaks, cracked casings, or fuel odors around the injectors indicate a problem.

Fixing Malfunctioning Fuel Injectors

In some cases, malfunctioning fuel injectors can be cleaned using a specialized fuel injector cleaner. If cleaning doesn’t solve the problem, you will need to replace the faulty injector.

While this job can be done at home, it requires a certain level of mechanical knowledge. If you’re not comfortable with it, a professional mechanic should handle the task.

Costs of Replacing Fuel Injectors

The cost of replacing fuel injectors varies greatly depending on your car’s make and model, as well as whether you choose to do the job yourself or hire a professional. Generally, a new fuel injector can cost anywhere from $50 to $300.

However, it’s worth considering having the injectors repaired. Many companies can fix them at a fraction of the cost of a new injector. But always ensure that the repair service is reputable to avoid further complications.

Check Engine Light Comes On, Potential Causes #3: Bad Thermostat

Bad thermostat. Thermostats are known to go bad after some time. It is smart to replace them when you do your water pump service. A bad thermostat may cause your car to overheat, and this heat may warp your engine block and the head of the block. Especially if it’s aluminum.

This can cost you hundreds or even thousands of dollars to fix. If it goes that bad that the engine is destroyed you will have to go on the market for a new engine. Depending on the car it may be very pricey.

Symptoms of a Failing Thermostat

There are several indicators of a failing thermostat that car owners should be aware of. One of the most prominent signs is overheating. A bad thermostat may not allow the coolant to circulate properly, which can cause the engine to overheat.

Another symptom could be fluctuating temperatures. If the thermostat is stuck open, the engine may run cooler than normal. On the other hand, if it’s stuck closed, the engine will overheat.

In addition, if you notice your car heater isn’t working correctly, this could also be a symptom of a failing thermostat. As the thermostat controls the amount of coolant that goes to the heater core, a malfunction could impact the heater’s performance.

Diagnosing a Bad Thermostat

Diagnosing a bad thermostat often involves observing the car’s temperature gauge. If it’s constantly high or fluctuating, there might be an issue with the thermostat.

You can also check the radiator hose. After the car has been running for a few minutes, one of the hoses should be hot (indicating that hot coolant is flowing from the engine to the radiator) and the other should be cooler (indicating that the coolant is returning to the engine). If both hoses are the same temperature, this might indicate a thermostat issue.

Fixing a Bad Thermostat

Fixing a bad thermostat typically involves replacing it. It’s usually best to replace the thermostat when you service the water pump to prevent it from failing in the first place. Replacing a thermostat can be done at home if you have some basic car repair knowledge. However, if you’re not comfortable doing it yourself, it’s recommended to hire a professional.

Costs of Replacing a Bad Thermostat

The cost of replacing a bad thermostat can vary based on your car’s make and model and whether you choose to do the work yourself or hire a professional. Generally, the cost of a new thermostat ranges from $30 to $100.

However, if your engine has overheated and caused further damage, the repair costs could escalate into hundreds or even thousands of dollars. So, it’s best to address a failing thermostat promptly to prevent more costly damage.

Check Engine Light Comes On, Potential Causes #4: Faulty Catalytic Converter

Catalytic converter failure. Catalytic converters are an essential part of your exhaust system, without them, you will never be able to pass emissions. They basically purify the exhaust gases that go out from the exhaust.

They block the NOx particles and make the car run cleaner and safer for the environment. The downside of these catalytic converters is that they clog up and it can be a very expensive fix to replace them. They can go bad after many miles and can trigger the check engine light in the cluster.

Replacing them sometimes is not a solution, and thankfully there are companies that clean these catalytic converters with high-pressure water and they can be good as new unless they are too far gone, in that case, you will need to open up your pocket, and get a new or used one.

Symptoms of a Failing Catalytic Converter

There are a number of telltale signs of a faulty catalytic converter. One is a decrease in engine performance. As the converter clogs, it can restrict the exhaust gases’ flow, reducing engine power and fuel efficiency.

Second, you might notice a rotten egg smell coming from your car. This is because the catalytic converter isn’t efficiently processing the sulfur compounds in the exhaust, leading to this distinctive odor.

Finally, you might observe a check engine light. The car’s computer monitors the catalytic converter’s efficiency, and if it’s not functioning properly, it will trigger the check engine light.

Diagnosing a Faulty Catalytic Converter

Diagnosing a faulty catalytic converter usually involves a diagnostic tool to read the fault codes stored in your car’s computer. The tool can pinpoint if the check engine light was triggered due to a converter issue.

Additionally, a visual inspection can also be helpful. A damaged catalytic converter may show signs of physical damage like cracks or holes.

Fixing a Faulty Catalytic Converter

Fixing a faulty catalytic converter depends on the extent of the damage. If it’s clogged, some companies specialize in cleaning these units with high-pressure techniques. This can restore the converter’s performance unless it’s too far gone.

If the converter is damaged beyond repair, replacement is the only option. While this can be done at home with the right tools and knowledge, many car owners choose to hire a professional due to the complexity of the task.

Costs of Replacing a Faulty Catalytic Converter

Catalytic converters are expensive to replace due to the precious metals used in their construction. Depending on the make and model of your vehicle, a new catalytic converter can range from $500 to over $2000, including labor costs. Cleaning a clogged catalytic converter can be a cost-effective alternative, but if the converter is beyond repair, replacement is unavoidable.

Check Engine Light Comes On, Potential Causes #5: Bad PCV Or EVAP System

Bad PCV valve. This check engine light that doesn’t shut off can be caused by a bad evaporative emissions purge control valve also known as a PCV valve, which is easy and cheap to fix DIY. A small thing that causes many headaches for car owners. Another reason may also be a bad evaporative emissions purge solenoid.

To sum up, if any of these issues are happening to you the engine light will be on all the time, if it flashes or it is on from time to time it is probably one of the issues that we are going to discuss in the next chapter.

Symptoms of a Failing PCV or EVAP System

The failure of the Positive Crankcase Ventilation (PCV) valve or Evaporative Emission Control (EVAP) system can produce several symptoms. If your car’s idle is rough or if you experience decreased gas mileage, it could be due to a bad PCV valve or EVAP system.

Additionally, you might see the check engine light staying on. While the check engine light could indicate various issues, a persistent light can often be traced back to a faulty PCV valve or EVAP system.

Diagnosing a Bad PCV or EVAP System

The PCV valve and EVAP system’s functionality can be checked using a specialized scan tool that reads diagnostic trouble codes (DTCs) from your car’s computer. If a problem exists within the PCV or EVAP system, the scan tool will likely pick up codes related to these systems.

For the PCV valve, a visual inspection can also help. The valve should be clean, and you should feel a slight vacuum when the engine is running. If not, the PCV valve might be faulty.

Fixing a Bad PCV or EVAP System

Fixing a bad PCV valve or EVAP system usually involves replacement. The PCV valve is generally quite accessible and can be replaced easily, often without tools. The EVAP system, on the other hand, can be more complex to repair due to its multiple components and their locations.

Costs of Replacing a Bad PCV or EVAP System

The cost of replacing a bad PCV valve is relatively low. The valve itself usually costs between $10 and $30, and if you’re comfortable with doing it yourself, you can avoid labor costs.

However, fixing issues within the EVAP system can be more expensive, as it often involves a professional mechanic due to the system’s complexity. Depending on the exact issue, you could be looking at costs ranging from $100 to $500 or more. Always obtain an accurate diagnosis to ensure you’re fixing the correct component.

Why Does My Check Engine Light Come On And Off

If this is the case you shouldn’t be worried, these problems may appear to any car owner. Some of these potential reasons are so simple, that you may even laugh at them at first. Although the cause of the issue may be simple, there is still the need for you to visit the local mechanic to fix these issues.

And, also prevent your car from illuminating the check engine light in the future. By this, we mean resetting the ECU of the car which is the main computer that controls everything. But first, let’s see what some of these issues are:

Check Engine Light Comes On Off, Causes #1: Loose Gas Cap

A loose gas cap, although hard to believe, and also sounds funny. Something like a loose gas cap may cause a disturbance in the check engine light. If you don’t tighten it all the way it may see the light come on, and the check engine light will stay on until you tighten your gas cap properly.

Also, check your gas cap for some issues. There might be cracking and uneven fitment if it’s some old cap that has seen better days. If the gas cap is bad just get a new one, they are really affordable.

Symptoms of a Loose Gas Cap

The symptoms of a loose gas cap are quite straightforward. If your gas cap is loose, cracked, or damaged, the most likely symptom you’ll notice is a lit check engine light.

You might also smell fuel. If the gas cap doesn’t seal properly, it can allow fuel vapors to escape, which can create a noticeable gasoline smell around your car.

Diagnosing a Loose Gas Cap

Diagnosing a loose gas cap is simple. If your check engine light turns on immediately after refueling, this is a likely cause. Check if your gas cap is tight.

It’s also essential to inspect the gas cap for physical signs of damage. Look for cracks or signs of wear, particularly on the seal, as these could also cause the check engine light to come on.

Fixing a Loose Gas Cap

The solution to a loose gas cap is easy: tighten it until it clicks. If the gas cap is damaged or worn, replacing it is the best course of action. This can be done easily by most car owners.

Costs of Replacing a Loose Gas Cap

A new gas cap is quite affordable, typically costing between $10 and $50 depending on the make and model of your vehicle. Replacing the gas cap yourself will save on labor costs. Remember, a loose or faulty gas cap can lead to a loss of fuel through evaporation, so this is a cost-effective fix that can also improve your car’s fuel efficiency.

Check Engine Light Comes On Off, Causes #2: Bad O2 Sensor

A bad oxygen sensor, now this may be an issue. Oxygen sensors are mounted on the front part of the exhaust right after the manifolds. They have an important role and that is to see how much exhaust gas is coming out of the exhaust.

They scan the data and send it to the ECU which checks the data and provides the right fuel to air mixture in the engine. A bad O2 sensor may cause your car to run rich on fuel. So it is better to address this problem right away because this is important for the car to run properly without issues.

If you delay this problem and don’t solve it the check engine will be permanent on your dash. Oxygen sensors are known to be expensive especially if you get a decent brand. Best advice, don’t go for the cheap ones, they will break after some time and your car will be broken again. Don’t save money on important stuff like this.

Symptoms of a Bad O2 Sensor

A failing O2 sensor can present several symptoms. You may experience decreased fuel efficiency as the sensor can’t provide accurate data to the car’s computer about the fuel-to-air ratio.

Additionally, you may notice a rough idle or even stalling, as the incorrect fuel mixture can disrupt normal engine operation. The check engine light will likely be triggered, as the car’s computer will recognize that the sensor is not functioning correctly.

Diagnosing a Bad O2 Sensor

Diagnosing a bad O2 sensor usually involves using a diagnostic scan tool to read fault codes from the car’s computer. An O2 sensor failure will usually trigger specific fault codes.

A professional mechanic can also use live data from the scan tool to observe the O2 sensor’s performance and confirm its failure.

Fixing a Bad O2 Sensor

Fixing a bad O2 sensor involves replacing the faulty sensor. While this is a task that can be done at home by a skilled car owner with the right tools, it can also be done by a professional mechanic to ensure it’s installed correctly.

Costs of Replacing a Bad O2 Sensor

Replacing an O2 sensor can be a moderate expense. The cost of a new sensor can range from $50 to $250, depending on the brand and type of sensor your car requires.

Labor costs can add an additional $50 to $150, depending on your location and the complexity of the replacement. As the O2 sensor plays a crucial role in your car’s performance and efficiency, it’s best not to skimp on this repair.

Check Engine Light Comes On Off, Causes #3: Worn-Out Spark Plugs

Bad spark plugs. Spark plugs can go bad after several thousands of miles, and they also can show you the check engine light from time to time. This happens because there isn’t enough spark in the combustion chamber and the fuel isn’t ignited.

This may cause your car to run badly or don’t even start, so replace your spark plugs if you want to solve your problems and avoid getting stranded somewhere where you don’t want to. Moreover, be diligent about the symptoms of loose spark plugs.

Symptoms of Worn-Out Spark Plugs

Symptoms of worn-out spark plugs can include a rough idle, engine misfire, difficulty starting the vehicle, and poor fuel economy. The engine might even fail to start. If the spark plugs are not creating the necessary spark to ignite the fuel in the combustion chamber, the check engine light can flash or remain constantly illuminated.

Diagnosing Worn-Out Spark Plugs

Diagnosing worn-out spark plugs may involve physically inspecting the spark plugs for signs of wear or damage. You can look for things like deposits, cracked insulation, or eroded electrodes. A scan tool can also be used to check for engine misfire codes that can point to a spark plug problem.

Fixing Worn-Out Spark Plugs

Fixing worn-out spark plugs involves replacing them. It’s a relatively straightforward process that can be done by a skilled DIYer or a professional mechanic. However, it’s important to ensure the new spark plugs are of the correct type and are properly gapped before installation.

Costs of Replacing Worn-Out Spark Plugs

The cost of spark plugs varies depending on the type your vehicle requires. Basic copper spark plugs can cost as little as $2 to $5 each, while platinum or iridium spark plugs can cost between $6 and $15 each.

Labor costs can range from $40 to $150, depending on the vehicle’s make and model, as some engines are easier to work on than others. However, considering the importance of spark plugs in your vehicle’s performance and fuel efficiency, this is a worthy investment.

Check Engine Light Comes On Off, Causes #4: Malfunctioning MAF Sensor

Bad mass air flow sensor. Mass airflow sensors or shortly known as MAF are well known to go bad after many miles, and also cause some check engine lights on your dashboard. The mass airflow sensor is controlling how much air is inserted into the engine and sends that data to the ECU.

This is a very important role that this sensor plays. If it’s completely broken you won’t be even able to start the vehicle, so fixing this sensor is a must. Always buy a quality sensor from a well-known manufacturer if you want your sensor to last and avoid paying twice.

Symptoms of a Bad MAF Sensor

Symptoms of a malfunctioning Mass Air Flow (MAF) sensor can vary, but they usually include poor fuel economy, rough idle, stalling, and difficulty starting. The engine may even refuse to start if the sensor is completely failed. The check engine light can be triggered as the car’s computer recognizes that the MAF sensor is not providing correct air intake data.

Diagnosing a Malfunctioning MAF Sensor

Diagnosis of a malfunctioning MAF sensor typically involves using a diagnostic scan tool to read the trouble codes stored by the car’s computer. These codes can indicate a problem with the MAF sensor’s operation. Additionally, a mechanic can view the live data from the MAF sensor via the scan tool to check if it is providing the correct air intake information.

Fixing a Malfunctioning MAF Sensor

To fix a malfunctioning MAF sensor, you’ll need to replace it. While this task can be done by a handy car owner, professional mechanics can ensure that the replacement part is installed correctly, and that the sensor is calibrated to provide the correct air intake information to the car’s computer.

Costs of Replacing a MAF Sensor

The cost to replace a MAF sensor can vary widely, depending on the make and model of your vehicle. The price for the part alone can range from $50 to $400.

Labor costs will depend on the complexity of the installation, but typically range from $50 to $200. Given the sensor’s importance in maintaining the efficiency and performance of your vehicle, it is an investment that will pay off in the long run. Investing in a quality part from a reputable manufacturer can prevent future failures and the need for further repairs.

Check Engine Light Comes On Off, Causes #5: Faulty EGR Valves

Exhaust gas recirculation valve. These valves are also known as EGR valves, and they are prone to many failures. If you have one on your car and you get the check engine light, this is probably the culprit for this situation. They have a role in lowering the amount of nitrogen oxide that comes out of the engine.

This also keeps it running efficiently in the process and reduces emissions. These valves easily get clogged up after 150 thousand miles and fail at this point. If you are into mechanics, you can take the valve away and give it a deep clean. If this works great, if it doesn’t you will have to spend around $150 for a good quality OEM one.

Symptoms of a Faulty EGR Valve

A faulty Exhaust Gas Recirculation (EGR) valve can cause your engine to experience issues such as rough idle, loss of power, poor fuel economy, and increased emissions. You might also notice a pinging or knocking noise – a condition known as pre-ignition.

When the EGR valve is not working properly, the check engine light can become illuminated or start to flash intermittently.

Diagnosing a Faulty EGR Valve

Diagnosing a faulty EGR valve often involves using a scan tool to read any trouble codes from the vehicle’s computer. These codes can point to an issue with the EGR system. Physical inspection of the EGR valve can also reveal carbon buildup or blockages that could affect its operation.

Fixing a Faulty EGR Valve

If the EGR valve is merely clogged, cleaning it may resolve the issue. This involves removing the valve and using a suitable cleaning solution to remove any carbon deposits. However, if cleaning does not work, or if the EGR valve is damaged, replacement will be necessary.

Costs of Replacing a Faulty EGR Valve

The cost to replace an EGR valve varies greatly, depending on the make and model of the vehicle. The price for a new EGR valve itself can range anywhere from $50 to $300.

The labor cost can add an additional $50 to $150 to the total, again depending on the complexity of the installation process. Although this repair can be an investment, it’s important for the overall health of your vehicle and to keep emissions within regulatory limits.

Can Low Oil Cause Check Engine Light To Come On

A common misconception is that if you run low on oil may cause the check engine light to come on. Many people believe in this, and let me tell you, it is wrong. Check engine does not have any connection with the oil level at all, check engine light usually turns off if there is something wrong with the ignition and the sensors.

For the oil level, you have the dipstick that you can check, and if you are not into that, or your car does not have a dipstick. If that’s the case an oil light will come on and warn you that you are running low on oil.

Also, if you are doing your services regularly, the car will remind you when it’s time for your next service on the cluster and will ask you to visit an official mechanic for your specific vehicle.

How To Fix A Check Engine Light

Nobody likes to have issues with their car and many people are more inclined to work on their vehicles rather than to pay a professional mechanic to do the job for them. Some people are doing this from the economic perspective of saving money. Others like me do it from passion and do not let anyone else touch their car. If you are one of those guys you will probably enjoy reading this.

Check Engine Light Comes On And Off

We are going to discuss some troubleshooting on how you can do this work at home with no expensive tools. Just simple DIY troubleshooting methods that will probably help you if your car has a check engine light that comes on and off, so follow along.

Step 1:

If your issue is caused by something trivial the easiest fix is probably removing the positive cable from your battery. By removing this cable, the computer will shut down and when you put the cable back on it should reset itself and should clear the codes. This is the simplest thing to do and one of the easiest fixes out there.

Step 2:

If the problem persists then you will need to grab an OBD2 scanner tool. These come cheap and will help you troubleshoot your issue, you will be able to clear the error and move on from there. When you start your car the check engine light should be gone and if it persists and reappears again, there is something more to it.

Step 3:

If your OBD2 tool is giving you the codes then search for them online to learn more about them. You need to do this research to get to the main issue. If you don’t get the codes on this OBD2 scanner you need to get a more advanced one.

An advanced scanner has more options and will allow you to dive deeper into the errors and will show you great detail of information. With this tool, you will be 99% sure that you will get the error.

Step 4:

If you found your problem, now is the time to deal with the issue. If there are bad sensors replace them with OEM parts, not get the cheap ones because you are going probably to have to pay twice in the near future because low-quality sensors are not good.

Step 5:

If it’s something with the ignition like spark plugs, coils, injectors. All of these things need to be addressed as soon as possible. You don’t want to get stranded on the road. More on that how you can replace these parts you can find online and there are some detailed guides on how to do this.

Just search on YouTube for how to replace spark plugs and there are plenty of sources out there that will help you out.

Step 6:

If it’s the PCV valve, just replace it with a new one. This is a simple and easy task to do, especially if you are into cars.

Step 7:

If the catalytic converter is bad then you need to get a used one or just find a service where these catalytic converters are cleaned and given good service. It should come out as a brand new when they are done with it. If it’s too far gone you will need to replace it with a new one.

Step 8:

A bad EGR valve, as it’s one of the main issues for this headache. If you are into mechanics you will search for ways how to remove it from the engine and then give it a good clean, if it doesn’t work you will need a new one or just get an EGR delete, and remove it completely.

Step 9:

For all of the things, we discussed above to work you need to clear off all of the codes after you are done with your car. Then the check engine light should be gone.

Reset Check Engine Light

Your car’s Check Engine Light (CEL) is more than just an ominous red or orange warning on your dashboard. It’s an alarm bell, alerting you that your vehicle’s onboard diagnostic system (OBD-II) has detected a potential issue. The root cause can be anything from a minor hitch such as a loose gas cap, to a more serious engine issue requiring professional attention.

Resisting the urge to ignore this light is critical. Although resetting it might bring temporary peace of mind, it’s like applying a band-aid on a wound that needs stitches. It’s essential to understand the cause before you attempt to reset the CEL.

The CEL operates on a simple principle: it lights up when the car’s computer (also known as the Electronic Control Module or ECM) detects a problem. If the problem is intermittent, the light may go off only to come on again when the issue reappears. Addressing the root cause of the problem is the key to keeping the light off permanently.

Now, let’s walk you through various methods of resetting the CEL, once you’ve addressed the issue causing it to light up.

1. Resetting the CEL by Cycling the Ignition

  • How it Works: Cycling the ignition involves starting and stopping your car a few times to prompt the computer to reassess the situation.
  • Procedure: Turn your ignition key to the ‘start’ position and allow the engine to run for a few seconds. Then turn the ignition off. Repeat this process three times.
  • Outcome: If the problem was resolved, the CEL should disappear. If it persists, further diagnosis or other methods of resetting may be required.

2. Battery Disconnection for ECM Reset

  • How it Works: Disconnecting the battery for a short period can erase the ECM’s memory, which includes the stored error causing the CEL to light up.
  • Procedure: With the car off and the key removed from the ignition, locate your car’s battery. Use a wrench to disconnect the negative (black) cable. Wait 15-20 minutes, then reconnect the cable and tighten it securely.
  • Outcome: This should reset the CEL. However, remember that this hard reset can sometimes lead to loss of settings or other electronic issues. It’s always advisable to check your vehicle’s manual or consult a mechanic before using this method.

3. Drive and Wait for Automatic Clear

  • How it Works: For minor issues, the CEL can turn off by itself after you’ve driven a certain distance.
  • Procedure: Continue your usual driving routine and watch the CEL.
  • Outcome: Typically, the light should reset and turn off within 30 miles of normal driving if the issue was minor and has been resolved. If the light persists, further investigation is needed.

4. Using an OBD-II Scanner for CEL Reset

  • How it Works: An OBD-II scanner reads the error codes stored by your car’s onboard computer. These codes trigger the CEL. You can use the scanner to clear these codes and reset the light.
  • Procedure: Locate the OBD-II port (usually under the steering column) and plug in the scanner. With your key in the ‘On’ position, press ‘Read’ on the scanner to read the trouble codes. Then select ‘Erase/Clear’ on the scanner to erase the codes.
  • Outcome: The CEL should reset. If the problem was addressed adequately, the light should stay off.

Cautionary Notes

Remember, resetting the CEL without addressing the root cause will only lead to the light reappearing. If the CEL persists after your attempted fixes and resets, it may be time to seek professional help. Avoiding or delaying essential repairs can lead to more significant problems and higher costs down the line. Being proactive about your vehicle’s health is the best policy.

And finally, a blinking or flashing CEL is a serious warning. If you observe this, it’s advisable to pull over safely and seek immediate professional assistance to avoid severe damage to your engine.

In essence, understanding your vehicle, diagnosing issues correctly, and resolving them promptly are essential steps in ensuring the CEL stays off, ensuring your vehicle’s longevity and your peace of mind.

Check Engine Light Meanings

Besides having the check engine light coming on and off, here are some other odd situations where you might find the CEL appearing…

Flashing Check Engine Light Then Stops

A flashing check engine light that stops can indicate a severe misfire in your vehicle’s engine. Misfires can damage the catalytic converter—a crucial part of your car’s exhaust system—if not addressed promptly.

To avoid costly repairs, reduce your speed and load (stop towing, if applicable), and have your vehicle serviced immediately. A diagnostic tool can pinpoint which cylinders are misfiring, assisting mechanics in resolving the issue quickly.

Check Engine Light After Oil Change

Seeing the check engine light after an oil change could be due to incorrect oil viscosity, an improperly installed oil filter, or the oil level being too low or too high. The first step is to check the oil level.

If it’s within the range, inspect the oil filter to ensure it’s correctly installed. The vehicle’s owner manual can provide specifics about the correct oil type for your car. If everything looks good, but the light persists, consult with a professional mechanic. It may be a false alarm or a more significant, unrelated issue.

Check Engine Light Went Off After A Week

If your check engine light turned on but went off after a week, it might be because the issue causing the light to turn on was intermittent or has resolved itself. It could range from a loose gas cap, which after a few driving cycles, secured itself, to fluctuating sensor readings.

However, your car’s computer stores these codes. A mechanic can use a code reader to diagnose the previous issue. Even though the light went off, it’s best to ensure there isn’t a lingering problem.

Car Shuts Off While Driving No Check Engine Light

Your car shutting off while driving with no check engine light can be quite alarming. This could indicate an issue with your car’s fuel system, ignition, or a failing sensor. To diagnose, check if your car has fuel and that the fuel pump is working.

If all is fine, your vehicle might have an ignition problem, such as a failing ignition switch or coil. In the absence of a check engine light, professional diagnostic tools may be necessary to find the issue. Consult with a mechanic to prevent further complications.

Check Engine Light On But No Codes

If your check engine light is on, but no codes are being read, it might be an issue with your car’s onboard computer or the code reader itself. First, verify the code reader is functioning correctly. If the problem persists, it may be an issue with the car’s computer.

A trained mechanic can check the car’s computer system for faults, ensuring the correct signals are being sent and received.

Car Struggling to Accelerate, Check Engine Light

When your car struggles to accelerate and the check engine light comes on, it typically indicates a problem with your vehicle’s performance. This could be caused by a clogged air filter, a failing fuel pump, or a malfunctioning sensor.

Check the air filter first; a simple replacement might fix the problem. If the problem persists, a diagnostic tool can identify any sensor issues. If these steps don’t resolve the issue, it’s best to have a professional inspect the fuel system.

Check Engine Light Turned Off by Itself

If your check engine light turned off by itself, it might be an intermittent issue that resolved itself. However, your vehicle’s computer will have stored any trouble codes. To ensure there are no lingering issues, have a professional mechanic run a diagnostic scan. They can pull up stored codes and address any potential problems, preventing further issues down the road.

Check Engine Light Came on While Driving

The check engine light coming on while driving can indicate several issues, from minor problems like a loose gas cap to more serious ones like a malfunctioning sensor or failing catalytic converter.

Don’t panic, but do reduce your driving speed and avoid hard acceleration. At the earliest opportunity, use a diagnostic tool or consult a professional to identify the source of the issue.

Check Engine Light After Getting Gas

If your check engine light comes on after getting gas, the most common cause is a loose gas cap. Make sure the gas cap is tight and secure. If the cap is damaged or missing, replace it promptly. Other possibilities include issues with your car’s evaporative emissions system.

If tightening the gas cap doesn’t resolve the issue, seek professional help to diagnose and rectify the problem.

Check Engine Light in Cold Weather

Cold weather can bring the check engine light on. It might be due to thickened motor oil, tire pressure changes, or a weakened battery. Check the oil viscosity, tire pressure, and battery health. If they all seem fine, the cold weather might have exaggerated an existing, undetected problem. A diagnostic scan can help uncover any lurking issues.

Check Engine Light Flashes Briefly Then Went Away

A check engine light that flashes briefly and then goes away might indicate a temporary misfire in the engine. It could be due to using low-quality fuel or a failing spark plug. Consider using higher-quality fuel or replacing your spark plugs. If the light returns or the vehicle shows other symptoms like stalling or rough idling, consult a professional.

Check Engine Light After Battery Change

After a battery change, your check engine light might come on. This could be because the onboard computer needs to relearn its idle and fuel trim strategy. This is normal and should resolve itself after some driving.

If it persists, check that the battery was installed correctly, and with all connections are secure. If the problem continues, it may be an unrelated issue and a professional diagnosis is recommended.

Tightened Gas Cap, Check Engine Light Still On

If you’ve tightened the gas cap and the check engine light is still on, it might be a damaged gas cap or a problem with the car’s evaporative emissions system. Replace the gas cap to rule out that possibility. If the problem persists, a professional mechanic can diagnose and repair the problem.

Permanent Code But No Check Engine Light

A permanent code without a check engine light is often due to a previous issue that was resolved but not cleared by the system. A diagnostic tool can identify and clear these codes. However, if the problem keeps reoccurring, further investigation is needed to prevent potential issues down the line. A professional mechanic can provide comprehensive diagnostics and appropriate repairs.

Driving With Check Engine Light On

You should definitely not be driving your car as it is. Just take it to your local mechanic. If you have the know-how and the right tooling then try to fix it on your own, although I would still recommend a professional mechanic. Especially if you do not know what you are getting into.

If the check engine light (CEL) in your car is flashing, it’s comparable to your body running a fever. It’s a symptom of an underlying condition that demands immediate attention. Just like neglecting a fever could lead to complications, ignoring the CEL could result in detrimental outcomes. Let’s delve deeper into the potential consequences of driving with a check engine light on.

1. Impact on Vehicle Performance

The CEL in your car signals potential issues within the engine or other crucial systems. Driving with the light on could result in performance deterioration, such as reduced fuel efficiency or power. This degradation can take a toll on your wallet and diminish the overall driving experience. An illuminated CEL might also indicate issues with the exhaust system, causing excessive pollution.

2. Risk of Serious Damage

Neglecting the CEL could allow minor issues to exacerbate into major, cost-intensive repairs. A simple issue like a faulty oxygen sensor, if not addressed promptly, might harm your catalytic converter. Given that replacing a catalytic converter could cost thousands of dollars, early intervention is a wiser approach.

3. Safety Hazards

Certain problems that trigger the CEL can pose serious safety hazards. For instance, a blinking CEL often denotes a misfire, which can dangerously overheat and damage the catalytic converter, posing a fire risk. It’s advisable to stop your vehicle and call for professional help if your CEL is flashing.

4. Violation of Emission Standards

In several states, a vehicle with an illuminated CEL might fail the emission test. Keeping the environment in mind and adhering to the law, it’s beneficial to address the issues indicated by the CEL promptly.

5. Decoding the Check Engine Light

Understanding the CEL’s behavior can provide insight into the severity of the problem. A steady light typically signals a non-emergency issue, although it should still be investigated. A flashing light, however, signifies a serious problem that requires immediate attention.

6. Immediate Steps to Take When Your CEL Comes On

Here are a few steps to take when your CEL illuminates:

  • Inspect for noticeable changes in vehicle performance or unusual sounds.
  • Check if your gas cap is tight. A loose gas cap can often trigger the CEL.
  • If your CEL is flashing, pull over safely and seek professional help.

7. The Importance of Professional Inspection

If the CEL illuminates, it’s crucial to seek professional help even if your vehicle seems to be running fine. A professional can utilize a special scanner to read the trouble codes stored by your vehicle’s computer, shedding light on the underlying problem.

In summary, while it might be tempting to ignore the CEL and hope it goes away, the risks and potential costs of doing so are significant. Regular maintenance and prompt response to the CEL’s warnings will save you time, money, and stress in the long run. Remember, it’s always better to be safe than sorry when it comes to your vehicle’s health.

Can You Sell A Car If The Check Engine Light Is On

You can try, but not many people would like to buy it from you. Especially people that are not mechanically inclined and are not into troubleshooting problems to find a fix. Even if they like to buy the car from you, they would love to get it at a cheap price. So better fix the check engine light before you sell.

Essential Facts

The check engine light in your car can turn on when there’s an issue. It doesn’t always mean a big problem, but you should fix it soon. Common issues include faulty ignition coils, fuel injectors, thermostat, and parts of the emissions system.

A loose gas cap can make the light blink on and off. If this happens, try tightening the cap. A broken oxygen sensor might also cause this. Fix it to avoid damaging the engine. Bad spark plugs can also trigger the light and mess with your engine.

A broken mass airflow sensor can lead to bad fuel economy and damage other parts. It can also make the check engine light blink. Don’t ignore the light. Find a mechanic to look at it.

If your check engine light blinks on and off, still get your car fixed. The problems can be as serious as when the light is always on. You can sell a car with the light on or blinking, but tell the buyer about the problem.


In this article, we went deep and learned a lot about this issue with the check engine light that comes on and off. We also thoroughly explained the main culprits for this issue. And finally, we shared some DIY fixes that will make your life easier. If you are a beginner, it is better to leave it to someone that is more experienced to deal with these issues, like a mechanic. But if you think you are ready just dive into it and start doing some troubleshooting.

Frequently Asked Questions

If you’re still curious about why your check engine light comes on and off, our FAQs here might help…

Why Is My Check Engine Light On

Your car’s check engine light may come on due to numerous reasons. Most of the time, it pertains to either your car’s engine or its emissions system. For example, a bad set of ignition coils or worn-out fuel injectors and spark plugs may prompt the check engine light to appear. Besides that, a malfunctioning thermostat, as well as bad O2 and MAF sensors (among many other sensors on your car) would also illuminate the check engine light if they failed. Otherwise, you might be seeing a check engine light because your catalytic converters are failing. Alternatively, it might be due to a clogged EGR valve, faulty EVAP, or broken PCV system. Even simple issues like a loose gas cap may prompt the check engine light to appear.

What Does Check Engine Light Mean

A check engine light is also sometimes known as the Malfunction Indicator Lamp (or MIL). Its function is as the name implies, it’s a warning light that appears to alert you if something’s amiss with your powertrain. For almost every car, it’s normal to see the check engine light (or CEL) appear when you’re putting and twisting the key in the ignition slot to turn your car on. However, under normal circumstances, the CEL should disappear in a few moments once your car has started. If the check engine light is still turned on, then it’s an indicator that your car has detected a fault. Thus, it’s a warning that you should diagnose whatever issues it’s found and have them fixed right away if it’s urgent.

What Does Service Engine Soon Mean

While all cars have a check engine light, some vehicles feature an additional warning light known as the Service Engine Soon light. In summary, a service engine soon light is often not as serious of an alert as the check engine light. While the check engine light turns on when serious issues are found, your car will turn on the service engine soon light if a lesser and more inconsequential problem is noted. Usually, these problems aren’t serious enough to cause significant damage to your car if not fixed soon. Besides that, some automakers also incorporate the service engine soon light as a reminder that your car’s scheduled service is due.

What To Do When Check Engine Light Comes On

First off, try to assess the status of the check engine light. If the check engine light is merely turned on and is illuminating in a yellow or orange color, it’s usually not something too serious. However, if the check engine light is blinking/flashing and is lit up in red, then you’ll have to get it diagnosed by a mechanic right away. There are some things that you can do to narrow it down and find what’s caused it to appear. Begin by seeing if there are any other warning lights or messages on your dashboard. For instance, if your car has low oil pressure or if it’s overheating. Then, try tightening the gas cap, as this may cause the check engine light to turn on. Other than that, you can plug in an OBDII diagnostics scanner to extract any error codes that’ll point you to the underlying issue.

How Long Can You Drive With Check Engine Light On

Whenever you’re seeing the check engine light illuminated on your dash, it’s often a bad idea to just ignore it and keep on driving. Although, this isn’t always the case. It ultimately depends on the seriousness of the problem that prompted the check engine light to appear. For example, if the check engine light is turned on but stays steady or is lit up in a yellow or orange color, it’s usually not something serious. Thus, if your car isn’t driving or behaving oddly, you may even be able to drive up to 50 or even 100 miles before sending it over to a mechanic. However, if the check engine light is blinking/flashing or is lit up in red, it’s normally telling you that a serious fault has occurred. To prevent imminent damage to your engine, it’s wise to send it over and have it checked ASAP.

How to Turn Off Check Engine Light

Turning off the check engine light involves addressing the problem that triggered it in the first place. You need to first diagnose the problem using an OBD-II scanner which will give you a code that corresponds to the specific issue. Once the problem is fixed, the light should automatically turn off. If it doesn’t, you can manually clear the code with the OBD-II scanner. If the problem isn’t fixed, however, the light will likely come back on.

Why Is My Check Engine Light Flashing

A flashing check engine light is usually a sign of a severe problem that could potentially damage your vehicle, such as a misfire that can overheat the catalytic converter. It’s recommended to stop driving the car and have it inspected by a professional mechanic as soon as possible to prevent further damage.

How to Clear Check Engine Light

The most effective way to clear the check engine light is to use an OBD-II scanner. Once connected to your car’s system, the scanner can read and clear the error codes causing the light to illuminate. If you don’t have access to a scanner, another method is to disconnect your car’s battery for a few minutes, though this can reset other systems as well.

How to Turn Check Engine Light Off

Similar to clearing the check engine light, you can turn it off by diagnosing the error code with an OBD-II scanner and rectifying the problem causing the light to illuminate. Once the issue is fixed, the light should turn off. If it doesn’t, you can manually reset the code using the scanner.

What Does a Check Engine Light Look Like

The check engine light is usually an orange or amber light on your car’s dashboard. It often features an icon of an engine or reads ‘Check Engine,’ although the design can vary depending on the car model. It’s part of the vehicle’s onboard diagnostic system, alerting you to potential issues with the engine or related systems.

How to Reset Check Engine Light Without Disconnecting Battery

You can reset the check engine light without disconnecting the battery by using an OBD-II scanner. Once you connect the scanner to your car’s OBD-II port, it can read and clear the specific error code causing the light to appear. If the underlying issue is not resolved, the light will likely turn on again.

How to Reset Check Engine Light Without Scanner

To reset the check engine light without a scanner, you can try driving your car for a certain distance and time. Some cars are programmed to reset the check engine light automatically after the car has gone through many cycles of driving and stopping. However, this might not work if the underlying problem has not been resolved.

What Does Check Emission System Mean

The ‘Check Emission System’ warning is part of your car’s onboard diagnostic system and typically indicates a problem with the vehicle’s exhaust system. This could involve issues with the catalytic converter, oxygen sensor, gas cap, or other parts of the system that helps regulate your car’s emissions. Any issues here can result in higher levels of pollutants being released.

What Sensors Can Cause a Car Not to Start

Various sensors can cause a car not to start, including the crankshaft position sensor, camshaft position sensor, and engine coolant temperature sensor. Other sensors such as the mass air flow sensor, throttle position sensor, and fuel pressure sensor can also cause starting problems if they malfunction.

Does Check Engine Light Come on for Oil Change

Typically, the check engine light does not come on for an oil change. However, if your vehicle’s oil levels are extremely low or if there’s an issue with your oil pressure, it could trigger the check engine light. Most vehicles have a separate indicator light for oil changes, often labeled as ‘service engine’ or ‘maintenance required.’

What Does It Mean When Your Check Engine Light Flashes Then Goes Off

If your check engine light flashes and then goes off, it typically indicates an intermittent problem. This could be due to a temporary issue that resolved itself, such as a loose gas cap, or it could be a more serious issue that’s only occurring under certain driving conditions. Even if the light goes off, it’s best to get the car inspected to avoid potential damage.

What Is the Most Common Reason for Check Engine Light

One of the most common reasons for the check engine light to come on is a faulty oxygen sensor. This sensor helps monitor how much fuel is burned. A faulty sensor can cause a decrease in fuel efficiency and increased emissions. Other common issues include a loose or damaged gas cap, a bad catalytic converter, and faulty spark plugs.

What Does Check Fuel Cap Mean

The ‘Check Fuel Cap’ warning light means that your car’s onboard diagnostic system has detected a leak in the evaporative emission system (EVAP), often due to a loose, damaged, or missing gas cap. Ensuring the cap is tightly secured or replacing it if it’s damaged usually solves the issue.

Does Replacing the Engine Reset Mileage

Replacing the engine does not reset the mileage of the vehicle. The odometer reading, which records the total distance the vehicle has traveled, remains the same even if the engine is replaced. However, it’s important to note the engine replacement in the vehicle’s service history. This can impact the vehicle’s value and performance.

How Long Until Check Engine Light Resets After Loose Gas Cap

If your check engine light came on due to a loose gas cap, it won’t go off immediately after you tighten it. The light should reset itself after you’ve driven the car for a while. Typically, after a few driving cycles. This can range anywhere from a few short trips to a couple of hundred miles, depending on the vehicle.

Can You Drive with Check Engine Light On

While you can technically drive with the check engine light on, it’s not advisable. The light is an indication of a potential issue with your vehicle. And, ignoring it could lead to more serious, costly damage. If the light is flashing, it indicates a severe problem, and you should stop driving and seek immediate professional help.

Can Bad Gas Cause Check Engine Light to Come On

Yes, bad gas can cause the check engine light to come on. If the fuel quality is poor, it can affect the engine’s performance and trigger the check engine light. Other fuel-related issues that can trigger the light include a clogged fuel injector. Alternatively, a failing fuel pump, or issues with the fuel pressure regulator.

What Are the Symptoms of a Bad Mass Air Flow Sensor

Symptoms of a bad mass air flow sensor can include a decrease in fuel efficiency, or difficulty starting the engine. Alternatively, an idling engine that stalls, or a check engine light that’s turned on. Your vehicle might also experience irregular acceleration or jerking during acceleration if the sensor is malfunctioning.

Why Does It Mean When Your Check Engine Light Comes On and Then It Goes Off by Itself

If your check engine light comes on and then goes off by itself… It often means that your vehicle’s onboard diagnostics system detected an issue that resolved itself. It can be a minor, temporary issue, such as a loose gas cap. Or, it could indicate a more complex intermittent problem. However, it’s advisable to have your car checked by a professional to ensure there are no serious underlying issues.

What to Do After Replacing Oxygen Sensor

After replacing the oxygen sensor, you should clear any diagnostic trouble codes from your vehicle’s onboard computer using an OBD-II scanner. Then, drive your vehicle for a few days. If the issue that led to the replacement was successfully fixed, the check engine light should remain off. If it comes back on, it indicates a persistent issue that needs further attention.

Why Is My VSC Light and Check Engine Light On

If both your Vehicle Stability Control (VSC) light and check engine light are on… It usually indicates an issue with your vehicle’s engine performance. Many vehicles are designed to automatically activate the VSC light when the check engine light turns on. This is because an engine issue could potentially impact the vehicle’s stability and traction control systems. It’s recommended to diagnose and fix the problem that’s triggering the check engine light to also turn off the VSC light.


  1. RoBo

    Great guide, easy to understand.

    1. Harry Gibson
      Zack Norman

      Thanks for the comment, RoBo!

      Cheers, glad our guide here has been of some help 🙂


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