Service Engine Soon Light

Service Engine Soon – What Does It Mean?

Imagine you’re thinking of going for a drive one day, and your fingers are just itching to turn on the ignition. But just as the engine roars into life, you notice a sudden glimmer come into view from your instrument cluster. You take a closer glance, and you notice it says, ‘Service Engine Soon’. At first, you might think to yourself, “Oh no, is something wrong with my car?”

The Service Engine Soon light has often been mistaken for the Check Engine light. The ‘Check Engine‘ light often means that something serious is wrong with your car. Meanwhile, the ‘Service Engine Soon’ light usually means that your car’s regular maintenance schedule is due. Understanding the difference, you might think that the Service Engine Soon light on your dash doesn’t necessitate anxieties.

Indeed, you shouldn’t need to worry as much, as it’s just the car’s way of gently reminding you to take it to the workshop for a check-up. However, it’s the small things that often lead up to big repairs. So, read along our guide here to know more about the Service Engine Soon light, what it means, and what you can do about it.

Service Engine Soon light - What does it mean?

What Is A Service Engine Soon Light?

So, you might have noticed that the Service Engine Soon light is glaring at you. Now, it’s time to understand what’s going on, and what does it mean. Besides, this light can even come along despite there not being any clear symptoms, or signs of problems. No odd sensations, vibrations, noises, smells, or leaking coming from the car. Alternatively, the more attentive among you might just have a sixth-sense that the car is a tiny bit off.

But it’s enough to make you wonder if anything is wrong at all. First, we must understand what’s prompting the Service Engine Soon light to come on in the first place. Pretty much every engine in modern cars have an electronic computer brain. They are called the engine control unit (ECU), or the engine control module (ECM).

They comprise of a small computer that sits within your car’s engine bay. It’s enclosed, like a plane’s black box. The ECU is then connected to many different sensors, all placed throughout the car and its key components. These sensors are able to sense, and analyse the inner machinations of the car to make sure everything is in working order.

Each component has its own threshold, and are designed to work best in its pre-set optimal states. The sensors are responsible for monitoring them, and then instructing other parts to work alongside it in unison. For example, being able to detect coolant temperature, accelerator pedal position, the flow and composition of air, and so on.

If, for instance, some of these components are running a bit too hot, too cold, or have signs of failing, the sensors will alert the ECU. If the ECU decides that something is wrong, it will alert you, the driver. This is done through the Check Engine, or the Service Engine Soon light depending on the car.

The engine control unit (ECU) controls and regulates the car's internal functions.

How Can You Learn The Difference Between The Service Engine Soon, And Check Engine Lights?

Going back to the previous section, we learned that issues within the car can prompt you with a warning. However, another confusion is that carmakers can sometimes combine both the Service Engine Soon, and the Check Engine lights. Consequently, many people mistake these two different indicators and use them interchangeably.

Any problems from within the car might prompt either light from coming on, but the key difference is in the severity of the issue. As such, we’ve highlighted the core meaning of what makes these two warning lights distinct from one another. Here are the differences, in greater depth.

1. ‘Service Engine Soon’ Light Explained

As the names suggests, the Service Engine Soon light usually warns you that your car is due for its usual maintenance. It lights up in text, showing ‘Service Engine Soon’, or ‘Service Due’. Alternatively, it could also light up when there are minor issues with the car, but are not immediate or catastrophic in nature. This is the reason why you might not be able to notice that anything is wrong at all with your car, when it lights up.

Carmakers can programme the Service Engine Soon light to come on after a set number of miles, or depending on when you’ve had it serviced prior. As robust as cars can be, every single component is still subject to wear and tear. This is given how complex a car is under the skin. It has a huge number of moving parts, constantly under strain.

Oils, coolant, spark plugs, fluids, air filters, and more might need servicing, or replacement. This is normal in the upkeeping process for any car throughout its lifespan. Therefore, you can be a bit more relaxed knowing that the car is simply reminding you that it’s time for a routine service. Once you’ve sent it to the workshop to have a check-up, they would reset that Service Engine Soon light.

The Service Engine Soon light is often a gentle reminder that your car's regular service if due.

2. ‘Check Engine’ Light Explained

Compared to the gentle reminder that usually comes with a Service Engine Soon light, this one is more of a loud klaxon. It often lights up in the shape of an engine, but can also appear as text. Seeing the Check Engine light is always a worry, and for good reason. It usually indicates that something is badly wrong with your car, and it needs immediate attention.

It might mean that a part of your car is failing, or malfunctioning, and you should have it checked up ASAP. This often relates to parts of the car that are responsible for the engine, transmission, or emissions control. Sometimes, it could be a sign that a sensor is broken. As we’ve learned earlier in our understanding of what a Service Engine Soon light is, sensors are important. It ensures that parts of the car is working in its most optimal state.

The result, is better efficiency and performance while keeping wear and tear at a minimum. It might not sound serious at first, but a malfunctioning sensor would allow a car to work beyond its threshold. This could possibly snow-ball into a more extensive problem down the line. Alternatively, the Check Engine light could mean that an entire component isn’t working well, altogether.

What’s Causing You To See The Service Engine Soon Light?

We now should be able to better differentiate the Service Engine Soon, and the Check Engine light. Next, we should try to dig up the root of the issue, and find out what’s causing it to light up. Once again, it’s worth pointing out that most carmakers would programme the Service Engine Soon light simply to show that the car is ripe for its regular service.

Nonetheless, we’ve seen some carmakers combine them under a single warning light, to indicate any and every fault. This could either be very serious, or nothing at all. We highly recommend that you consult your car’s owner’s manual, and understand how your carmaker has programmed the light in. Or, give a call to a dealer or mechanic to understand more.

This should let you know distinctly what might cause the Service Engine Soon, or Check Engine light to turn on. In order to give you a wider, and more general look into the potential cause, we’ve combined them into a single warning beacon. Now, we’ll be looking through the issues that might prompt either light to come on, in order of severity.

1. Routine maintenance alert

Some things need changing, or checking up on every once in a while. Every car requires a scheduled service after a set amount of time, mileage, or usage. For example, replacing an air filter, or changing the engine oil. The Service Engine Soon light was created purposely to remind you of this. It’s a reminder that you should have it checked at your nearby mechanic or dealer, as soon as you can.

2. Loose, or faulty fuel-filler cap (fuel cap, or gas cap)

This is the simplest of issues that could cause your Service Engine Soon light to appear. The ECU or ECM can sense that your fuel cap is either lose, or is faulty. The fuel cap ensures that the fuel tank is properly sealed. It works both ways. Nothing can get into the fuel tank, ensuring that it does not contaminate the fuel. And, it also works to make sure fuel – or fumes – does not leak outside.

3. Low amounts of fluid

A car has many moving parts. To make sure that it all works smoothly, and to regulate against wear and tear, a car has copious amounts of fluids. Engine oil, coolant, brake fluid, transmission fluids, and more are among the liquids inside a car. It the levels of these fluids are low, it might prompt the Service Engine Soon light to appear. Low fluid levels could either be a sign of a leak, or just overdue for a top-up.

Low fluids, such as engine oil, could be a reason for warning lights to come on.

4. Spark Plugs in need of changing

Another cause for lighting up either the Service Engine Soon, or Check Engine light is the state of your car’s spark plugs. Spark plugs are what ignite the mixture of compressed air and fuel within the combustion chamber. The spark creates an explosion, which then creates energy for your car to move around.

Spark plugs are often designed to last a long time, and can easily keep working without issue for 100,000 miles or more. However, they do need changing eventually to make sure the combustion process is working at its optimal state. A faulty or failing spark plugs can cause a deterioration in performance, such as misfiring or poor acceleration. It can also cause increased fuel consumption, or the car not starting properly.

5. Oxygen Sensor failure

For internal combustion engine (ICE) powered cars, it’s important for the engine to ensure that the air-fuel mixture remains optimal. This is what guarantees the engine to not only operate smoothly and with adequate performance, but also efficiently. The oxygen sensor (O2 sensor) is responsible for keeping this in check.

It does this by monitoring the amount of oxygen that has been exhausted from the engine, and informs the ECU or ECM. If the O2 sensor fails, the engine could either be burning the fuel with too much (lean), or too little (rich) oxygen. The end result is subpar performance, poor fuel efficiency, and increased emissions. An O2 sensor failing would prompt the Check Engine light to come up, normally.

Spark plugs, although designed for a long time, will eventually need replacing.

6. Mass Air Flow Sensor failure

The Mass Air Flow sensor, or MAF sensor, works on the opposite end of the O2 sensor. It is just as important, as it informs the ECU or ECM to know much fuel to pump into the engine, depending on the intake composition of the air. The air changes in its density depending on variables such as the temperature, and pressure.

Hence, its very important for the MAF sensor to tell the engine how much fuel is required. If it’s working as intended, it should alert the engine as to how much fuel is required. The end result is a clean and efficient burn. If the MAF breaks, the ECU would miscalculate the amount of fuel that is injected. Not only would this cause damage to the engine, but also results in the same problems caused by a faulty O2 sensor.

7. Catalytic Converter failure

This is by far among the most serious causes that could light up the Service Engine Soon or Check Engine lights. Burning fossil fuels, such as petrol or diesel, releases loads of harmful gasses into the atmosphere around you. This is made worse for the air, as particulates are released caused by the use of toxic chemicals during the refining process of fuels.

This is why most cars have catalytic converters, placed within its exhaust system. Catalytic converters work to scrub off the harmful chemicals and pollutants that are released from the engine. Catalytic converters, although designed to last a long time, can wear out over time. This is especially if you continue to drive a car for extended periods with failing O2 and MAF sensors.

Should You Keep on Driving With A Service Engine Soon Light On?

We now know that causes that could prompt either the Service Engine Soon, or Check Engine lights to come on. Now we come to the question of should you keep on driving with one, or either lights blinking along? The answer is a bit complicated.

First, we should know that the Service Engine Soon (and the Check Engine) light may have multiple different states. If its simply lighting up in yellow, orange, or an amber shade, then it might not be serious. However, if its flashing or blinking, or changing its colour to red, then its warning you that the car needs immediate and serious attention.

In the end, it’s a matter of understanding how your respective car manufacturer has programmed in what to inform you, whenever either the Service Engine Soon or Check Engine light comes on. As such, we highly recommend that you consult your owner’s manual to understand more specifically. However, our general view is that you should stop driving, and have your car looked at as soon as possible.

You should think twice before driving with a Service Engine Soon light on your gauge cluster.

But Can You Just Ignore It, And Keep On Driving?

“But can I just ignore it, and keep driving?”, you might wonder. The Service Engine Soon light, as we’ve learned already, often indicates minor problems, or serves as a reminder for routine servicing. However, we also know that small problems can quickly, and expensively lead to bigger problems if not resolved quickly, and properly.

Our recommendation is that you be wary of driving your car, and probably only drive as a last resort. After all, a car is a very complex machine, and all the hundreds and thousands of moving parts need to work in unison. Just a single fault, and it would put more strain, thus causing damage on other components. It would also result in the car not working properly, thus affecting performance, fuel efficiency, emissions, and so on.

For example, let’s put ourselves in the scenario of being late to work, and needing to get there fast. You start up your car, and notice an amber light that says ‘Service Engine Soon’. In this scenario, it should be okay for you to keep driving gently, and send it off for a check-up on the way home later. But while driving, be attentive to any slight changes in behaviour of your car, and do take note. Still, we recommend that you have it checked right away.

In our second scenario, let’s consider the same being late to work example again. But this time, you notice a flashing ‘Service Engine Soon’ light, or it lighting up in red. In this case, we highly recommend that you don’t drive. Any further use of the car while the ECU is detecting some fault would eventually lead to more damage, or wear and tear down the line. What could be a simple issue, might result in bigger bills later on.

Can You Diagnose A Service Engine Soon Light?

You might wonder to yourself then, that there are many potential problems, both big and small, which could light up the Service Engine Soon warning. I’m sure you ought to be curious on how you could try to narrow down the problem a bit further. If anything, narrowing down the cause might just be a good way for you to plan out on how much you need to withdraw from the ATM to have your car fixed.

Your car’s owner manual should have an explanation, and hopefully an easy-to-read list. This would show all the problems that could arise, if the Service Engine Soon or Check Engine light were to come on.

Alternatively, most modern cars have on-board diagnostics. You can then use an OBD scanner that is compatible with your car. If your car is younger than 15 years old, then it might be compatible with the newer OBD2 standard. You can find these rather cheaply, often much less than $100.

There are even Bluetooth enabled OBD scanners, allowing you to monitor them from your phone. Plug it into your car to read precisely what error codes are being thrown up by the ECU. This could easily pinpoint more precisely as to what’s causing the Service Engine Soon light to come on. It could also make for an easier way for you to understand more on what needs to be done, so you can find the right technicians to fix it.

You can always diagnose issues on your car with an OBD2 scanner/reader.

Can You Fix The Causes For A Service Engine Soon Light?

But let’s say you don’t want to send it over to a workshop or dealership to have it fixed. Besides, labour costs are quite hefty given what needs to be done, especially if the Service Engine Soon light is showing only minor problems. If you have the time, there are some things that you can do very easily and quickly to fix the problems at home.

1. Loose fuel cap

This is by far the cheapest cause for the Service Engine Soon Light to come on. Simply turn off the engine, remove the fuel cap, and tighten it back up again. Maybe you just forgot to have it screwed around the whole way through the last time you filled up your car.

Now, start the engine, and see if the Service Engine Soon light goes away. Note, it might not immediately disappear, and would require you to drive around for a bit before it does. If the light still doesn’t disappear, then the ECU may have detected that the fuel cap needs to be replaced. You can quickly buy a replacement for between $10-$20.

2. Low fluid levels

You can very easily check and fix this one too, while you’re at home. Turn the engine off, and check the engine bay to find all the tanks and reservoirs as needed. You can consult the owner’s manual for some help to find them. Then, check the engine oil, brake fluid, coolant, transmission fluid, and even the windscreen washers to make sure.

Every reservoir should have a marker to show the minimum level of fluid needed. If its too low, then you can consult your owner’s manual again to see which brand of fluid is recommended. Have it topped up, and see if the Service Engine Soon light goes away. Although, low fluid levels could also be a sign of more extensive problems, such as leaking, or needing to completely change and flush some of the fluids.

Keeping your car's fluids topped up is a good way to prevent wear and tear.

Could I Just Send It Over To A Mechanic, Instead?

You might be reading that, and thinking maybe, just maybe, its a bit too serious for you. Or maybe you just aren’t sure about your way around a car, or aren’t confident enough to fix it yourself. No worries, as there’s a wealth of different options out there, with experienced and caring technicians to do the work for you. If you’re in the US, you can use sites such as OpenBay, or YourMechanic to find quotes from nearby garages.

They are, naturally, a bit more of an expensive option given the addition of labour. But, the added expense might just be worth it to make sure your car runs smoothly and trouble-free for a few more years. The best source we have to know how much these parts will cost is using CarMD. You can look through their most recent report here, to find out the average causes and fixes for problems pertaining to the Service Engine Soon light.

The most common fault on average is a failing O2 sensor. These can cost an average of around $250, including the cost of labour. Spark plugs averaged around $170, although it’s worth noting that this depends on how many your car needs. One spark plug per cylinder, and you can readily find them online for under $10 each. An MAF sensor would cost you a hefty $345, while a new catalytic converter is an eye watering $900!


In conclusion, we hope that you’ve learned a thing or two about the Service Engine Soon light. Hopefully, you’ll be better prepared the next time, if it ever lights up on your instrument cluster. A Service Engine Soon light, in short, is like a canary in a coal mine. It chirps along if something is amiss. Pay no heed for long enough, and you may be walking into a world of hurt.

It might be something as minor as a loose fuel cap, or it might require entire sensors replaced. Expensive as it may be, sucking up the expense for now may as well help to avoid even ruinous repair bills later on. It’s a reminder to always keep on top of your car’s condition. It’s just like practicing your own healthcare routine, maintaining good exercise and a healthy diet.

If you practice the same care and due diligence on your car as you do with yourself, then you might never have to see that Service Engine Soon light. Always be attentive to even the smallest of problems, or if your car is behaving oddly. Do that, and your automotive companion will never let you down.

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1 Comment

  • My service engine soon light is on and had it tested and it said my output speed sensurIis bad and my car is having trouble off and on coming out of gear winding up r.p.m.s

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