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Service Engine Soon Light | Why It’s On & How To Fix It

Your car’s computer is capable of detecting many types of problems with your engine. From misfires to failing sensors, the computer will warn you of potential issues. When the computer detects a problem, it will illuminate the Service Engine Soon light (SES). This warning light should not be taken lightly, and you should always read the trouble codes to determine what triggered the warning. There are a few common reasons why the light will come on, and we will tell you what those are. In addition, we’ll also tell you how to fix things so the light goes off for good.

8 Most Common Causes Of Your Service Engine Soon Light

If you are wondering, “Why is my check engine light on,” we have the answer! Some causes of the light are extremely simple, while others are more complex to diagnose. When you see that light pop up on your dashboard, one of these things probably caused it. Here is a list of the most common causes of the SES light.

— Engine Misfires

Engine misfires are probably the most common culprit of the check engine light. Misfires can occur for a variety of different reasons, like old spark plugs, bad spark plug wires, a faulty ignition switch, or even bad gas. A misfire simply means that the ignition inside a particular combustion chamber did not happen at the right time. A single misfire in one cylinder is not usually a major cause for concern, but multiple misfires usually signal a problem. If you read the trouble codes from the car’s computer, it should point you to the specific cylinder where the misfire occurred. Troubleshooting misfires can sometimes be difficult, but start with the easiest things first – like bad spark plugs or dirty fuel injectors.

— Bad Gas

On its own, bad gas will not set off your check engine light. The car’s computer cannot detect that the gas inside the gas tank is bad. However, bad gas leads to other problems that will cause the SES light to come on. Specifically, bad gas will cause engine misfires. As we already mentioned in the previous section, misfires are one of the leading causes of a check engine light. Bad gas will not ignite properly inside the combustion chamber, and a misfire will occur. When this happens, you can certainly expect the warning light to illuminate.

— Loose Or Faulty Gas Cap

The check engine light in your car could illuminate due to something as simple as a loose gas cap. If you refill your car with fuel at the gas station and do not tighten the cap properly, you might see the check engine light when you restart your vehicle. The light is meant to warn you that the cap was not tightened properly. Some people think that perhaps a different light would be a better signal, but most manufacturers use the check engine light to notify drivers of this condition. In some cases, the cap may even be faulty and need a replacement.

— Fouled Spark Plugs

Spark plugs don’t last forever, and they will need replacement when they go bad. Spark plugs can go bad due to age as they simply become worn out. Additionally, spark plugs can become fouled out if oil gets inside the combustion chamber due to bad piston rings. Either way, a fouled plug will not fire properly. When this happens, a misfire will occur, and the check engine indicator light will come on. A bad ignition coil will also lead to the warning light coming on. You should refer to your owner’s manual to determine how often to change your spark plugs. Although replacing the plugs is usually a scheduled service item, they do not need to be replaced very often. The cost to replace bad spark plugs is generally less than $800 in most vehicles.

— Bad Oxygen Sensor

Oxygen sensors are placed throughout your car’s exhaust system, and they relay important emissions information to the vehicle’s computer. These sensors measure the emissions both before and after the catalytic converters in the system to make sure the converters are working properly. If one of these sensors in the emissions system fails, that could be the reason why your check engine light comes on. Although a faulty oxygen sensor is not always a serious problem, you should get it fixed as soon as possible to avoid bigger problems down the road. A bad catalytic converter can also cause a check engine light to come on, and a bottle of catalytic converter cleaner can often fix that problem.

— Malfunctioning Mass Airflow Sensor

There is a sensor in modern cars located between the air filter, and the throttle body called the mass airflow sensor. This sensor measures the amount of airflow entering the intake, and the data from this sensor is used to determine how much fuel needs to be delivered by the fuel system. A faulty mass airflow sensor can lead to engine trouble, and it will also lead to a check engine light. If your car isn’t running right and you see a check engine light, the mass airflow sensor might be to blame.

— Low Fluid Levels

If you wonder what the service engine soon light means, it could indicate low fluid levels. Your car’s engine relies on different fluids to keep it lubricated and cooled. Engine oil and coolant are critical to a properly working engine. So, a low coolant or oil level could be detrimental. If these fluid levels get low, your car’s computer will alert you right away. This is not a minor problem, and you should get your car to a repair shop right away. Fluid levels should always be checked as part of routine maintenance. If you notice that a certain fluid is regularly low, you have a leak and should investigate the cause of the problem.

— Overdue Maintenance

Regular maintenance, like an oil change, is necessary to keep your car running properly. Most modern cars have reminders to let you know that it is time to perform maintenance. The onboard diagnostics will let you know that maintenance is due, and sometimes the notification method is the Service Engine Soon light. Some car owners choose to perform this maintenance on their own, and others head to their local auto repair shop. Either way, remember to clear the error codes after the maintenance is performed so the light will go away.

What To Do If Your Service Engine Light Comes On

If you see the Service Engine Soon light, you are probably wondering, “Why is my engine light on?” You probably also want to know what you should do about it. As long as your vehicle is still running like normal, the engine light likely does not signal a critical issue. Get your car to a repair shop as soon as you can so they can read the error codes from the computer.

Once the error codes are obtained, a mechanic can use those codes to tell you why the light came on. A quick Internet search will usually tell you what the code means as well. Just search for your car, like a Toyota or Nissan, along with the error code, and you should easily be able to find out what the code means.

Once you have found the cause of the light, you should be able to determine what will be required to fix it. If a faulty part causes the issue, like a bad oxygen sensor or mass airflow sensor, then you will need to replace the part to fix the problem. However, if the light was caused by an engine misfire, more troubleshooting might be required to determine the root cause. In some cases, you might even have to replace a few parts before finding the specific problem that caused the light. Once the issue is fixed, you can reset the light and drive like normal. We will tell you how to reset the light in the next section.

How To Reset Your Check Engine Light

Now that the problem has been identified and fixed, it is time to reset the check engine light. There are a couple of ways you can do this. The best and most proper way to reset the light is by using an automotive scan tool. Connect the scan tool to the OBD II port and use the tool to reset the light. If you visit a repair shop, this is the method they will use to reset the light.

However, not all car owners have their own scan tool. If you fixed the problem yourself, you might need another method to reset things after the service engine soon light comes on. You can reset the light without a scan tool by disconnecting the negative battery cable. Disconnecting the battery will interrupt power to the computer, and the stored error codes will be lost. Simply leave the cable disconnected for 15 to 30 seconds and then reconnect the battery. If the problem that caused the light was fixed, then the light should not reappear when the vehicle is restarted.

The Bottom Line

If you wonder, “Why is my engine light on,” there could be a few different causes. Anything from a loose gas cap to bad spark plugs could cause the light to illuminate. However, reading the trouble codes from the computer should point you in the right direction. Once the problem is fixed, simply reset the light with a scan tool or disconnect the battery. The light should go away, and you can drive your car worry-free!

Frequently Asked Questions (FAQs)

Can I drive with the ‘service engine soon’ light on?

Yes, in most cases, you can still drive your car with the service engine soon light on. As long as your vehicle runs normally, you can continue to drive the car. However, you should not just ignore the light. The light came on because a problem was detected, so you should determine the cause of the problem and have it fixed. Driving for extended periods of time with the light on could cause further damage and lead to big engine problems.

Can a service engine soon light mean you need an oil change?

Yes, some vehicles will illuminate the service engine soon light when it is time for an oil change. Other routine maintenance items can also trigger the light. Your local auto repair shop can read the error codes and determine the cause of the light. Once the oil is changed, the light can be reset, and it will go off until another problem is encountered.

How long does it take for the service engine soon light to go off?

The service engine soon light will typically not go off until the problem that caused the light has been fixed. As long as the problem continues, the light will stay on. Once the repair has been completed, the light can be reset with a scan tool or by disconnecting the battery. The light should go off immediately after it has been reset. As long as the problem is fixed correctly, the light should not come back on unless another problem occurs.

How is the service engine soon light different from the check engine light?

So, “What does service engine soon mean,” and is that different from a check engine light? Typically, the service engine soon light signals the need for upcoming maintenance, like an oil change. However, what does the check engine light mean? The check engine light usually points to a mechanical problem, like a bad sensor or an engine misfire. The terms are often used interchangeably by many people, but some vehicles draw this distinction between the two lights.

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