One of the great things about cars today is that they have computers that can tell you what’s wrong with them. The bad thing? The computer doesn’t actually tell you what’s wrong with the car. It’s frustrating, you’re driving along and the check engine light pops on. The purpose of this light is to tell you that something is wrong. But what? Is it minor? Is it serious? Will I be stranded? Will my car blow up?

Take a deep breath. Most of the time, the check engine light is indicating a minor problem. However, that doesn’t mean that you should just drive all around town without paying any mind. To help calm your nerves and narrow down your list of potential problems, we’ve put together this nifty guide to help you know what are the most common causes of the check engine light.

You Need New Spark Plugs

Spark plugs are a fairly simple little contraption that protrudes into the engine’s combustion chamber and makes a tiny spark which ignites the fuel inside the engine. This combustion action is what provides force to the engine, but it can’t start up all on its own. The spark plug provides the tiny amount of energy that leads to the explosive force that powers your car’s engine.

If your spark plugs are bad or firing incorrectly, your check engine light may illuminate. If you experience a jerky acceleration when you put your foot on the gas pedal then the spark plugs or spark plug wires are the most likely culprits. 

There is one good thing about spark plugs triggering the check engine light to come on. They are probably one of the cheapest parts you will ever need to replace in your vehicle. Not only that, but you can change a spark plug in only a few minutes! So in a way, needing new spark plugs is a good problem to have.

You Have A Bad Ignition Coil

We discussed how the spark plugs deliver a spark to the combustion chamber of your internal combustion engine, but the spark plugs need something to make them spark in the first place! This is the job of the ignition coil. This consists of a group of wires that coiled together. They take a small electric charge from your car’s battery and magnify it into a much larger charge. It then stores this electrical energy awaiting the moment the car’s computer brain sends the signal to release it. When that stored energy is released, it causes the spark plug to ignite the fuel in the combustion chamber.

After years of use, ignition coils can become faulty. If the rubber around the ignition coil degrades, all that stored up energy inside the coil can go awry, arcing to other metal parts inside the engine. This in turn dilutes the power of the electrical charge that is meant to be delivered directly to the spark plug.

Most cars have one ignition coil per spark plug, and for most cars the switcheroo is pretty simple and straightforward. You are most likely looking at around $20 per ignition coil, unless you have a high performance vehicle. In that case, you may expect to pay as much as $250 per ignition coil.

You Need A New Mass Airflow Sensor

If you are like most people, you probably are not replacing the air filter inside your engine very often. This can be a problem because the combustion process happening under the hood needs 3 things- fuel, a spark, and oxygen. 

The computer in your car needs to know how much air is coming in so it knows how much fuel to inject into the combustion chamber in order to get that perfect fuel-oxygen mixture for peak performance. If you don’t change your vehicle’s air filter often enough, you could cause the mass airflow sensor to malfunction and relay faulty information to the car’s computer brain. This will ultimately lead to poor performance, low gas mileage, and increasing emissions of pollutants and greenhouse gasses.

If you need a new mass airflow sensor, you are going to be looking at about $200 for the sensor itself, plus labor for the shop or mechanic. We did the math and we figured out that spending $15 for a new air filter and making sure you get it changed out annually will save you a bunch of cash.

You Have A Faulty Catalytic Converter

Have you ever been driving down the road and smell something like rotten eggs? And you think, where could there possibly be a bunch of rotten eggs out here on the highway? That is the smell of a catalytic converter that has gone bad. You see, the purpose of a catalytic converter is to filter your exhaust. The catalytic converter uses precious metals to convert carbon monoxide and other noxious emissions into other compounds which are better for people and the environment. 

Most times your catalytic converter will last the lifetime of your vehicle, or as much as 300k miles. However, if the catalytic converter goes bad it can lead to lower fuel economy, poorer performance, and the smell of rotten eggs. If your catalytic converter becomes seriously clogged it could cause your engine to stall all together, leading to you stranded on the side of the road.

While it may be easy to diagnose a bad catalytic converter, replacing one is unfortunately not easy. Due to the fact that its internal components are made up of precious metals, a new catalytic converter can cost you upwards of $1000. And that’s not all. A catalytic converter is not like a spark plug that is so easy to replace my grandma can do it. You are going to need an experienced mechanic for this one.

You’re In Need Of A New Oxygen Sensor

One of the most common causes of the check engine light popping up is due to a faulty oxygen sensor. This device has become a standard feature in all vehicles manufactured after 1980. This sensor makes sure that your vehicle is burning the right amount of fuel in order to achieve maximum performance.

With regular use this sensor will eventually get gunked up. When the sensor is clogged it will not be able to do its job properly which will trigger the check engine light. Your local mechanic can fix it for you in exchange for around $200. If you like getting under the hood, you may be able to do this job yourself and save a few bucks.

Your Gas Cap Is Loose

This fix is even easier than replacing a spark plug! When you replace the gas cap after fueling up, you want to screw it in until it clicks several times. That is to say, keep twisting about a quarter turn after you feel like the cap is already tight. 

It may seem a little ridiculous, but failure to properly screw on your gas cap can throw your vehicle’s emission system completely out of whack! This is because the fuel vapors are allowed to escape from the gas tank.

So, if your check engine light comes on when you’ve recently filled up your gas tank, try giving the gas cap a twist until you hear a few clicks. If your gas cap is damaged or faulty, you can find a new one online for about $10.

You Have Faulty Fuel Injectors

Most cars these days have a small valve that is controlled by the car’s computer brain called a fuel injector. Unless you’re driving a Nascar, your vehicle probably has one injector per cylinder. Its job is to regulate the flow of fuel into the combustion chamber and ensure a good fuel-oxygen mixture.

Whether you fill up with the cheapest gas, premium octane, or diesel fuel, most all gas has impurities in the mix. The impurities in the gas as well as residue created in the combustion process can cause gunk to accumulate in and around the tips of the fuel injectors. When this happens, the injector may only be allowing through some of the fuel that is intended to be sprayed into the cylinder. In severe cases, the injector tip may become completely clogged blocking the flow of fuel entirely, or get stuck open allowing way too much fuel to pass into the combustion chamber.

If you are experiencing a rough idle, or have cylinders that are misfiring when you accelerate, the culprit may likely be a clogged fuel injector. Fuel injectors play a very important role in the internal injection process and are very precise instruments. As a result, they can be expensive. The cost of replacing a fuel injector can cost you over $700.

You Have A Vacuum Leak

Many vehicle systems require a vacuum to help with their functions. These include things like the power braking mechanism, throttle, and emissions systems. Valves and hoses that are associated with these components get negative pressure gradients for the intake manifold of the engine.

A number of things can lead to a decrease in this vacuum pressure. It could be a valve that is stuck open or closed, hoses that have become damaged or dislodged. When that happens, the car’s computer will register a loss of vacuum pressure, triggering the onboard diagnostic system – that’s the check engine light.

Diagnosing this problem is going to require the expertise of a skilled mechanic. The fix could be as simple and inexpensive as reconnecting or replacing a hose that has become loose or cracked. It could also be something like a cracked intake manifold, which could end up costing you upwards of $1000. The only way to tell for sure will be to have it looked over by a qualified auto mechanic who can run a full diagnostic.

You Have A Bad Thermostat

The engine thermostat plays an important role helping your vehicle to operate right in the sweet spot for temperature. The optimal temperature for an internal combustion engine to operate at is right between 195-220 degrees fahrenheit. If your engine temperature is too low, you could be getting poor fuel economy. Too high, and you could be releasing an excess of harmful emissions into the atmosphere.

In order to stay right in the optimal temperature zone, the thermostat works to control the temperature of the coolant within the engine. When the engine temperature is inside the proper range, the thermostat allows for coolant to flow in the engine. When the engine cools below the prime operating temperature, the thermostat halts the flow of coolant.

The thermostat is a relatively rudimentary device, but like everything in your car, it’s liable to wear out eventually. The check engine light may illuminate if the thermostat isn’t working properly. Luckily, replacing a thermostat is pretty straightforward. If you are handy and have some basic tools you may be able to replace the thermostat yourself without too much trouble. If you prefer to leave these types of things up to the professionals, you can expect to pay around $200 all said and done.

While often the appearance of a check engine light is no big deal, it’s not something that should be ignored. If you leave the issue causing the check engine light to come on for too long, you could risk turning a small problem into a major repair. If you notice the check engine light in the dash of your vehicle, don’t hesitate to call Inland Mobile Mechanic. You don’t even have to go through the hassle of taking your car into the shop. We can easily diagnose your check engine light while you are out to lunch!