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BMW Check Engine Light – Why Does It Turn On?

by Jordan Harris
BMW Check Engine Light

Are you started experiencing some issues with your BMW? The BMW check engine light is probably the first notification that you got on your dash. But what does this check engine light mean? We are about to find out in this article and more.

Troubleshooting is a mastery by itself and knowing to troubleshoot will set you few steps ahead of everything. Knowing to troubleshoot will give you that extra edge in discovering problems on your vehicle.

Many mechanics out there misdiagnose problems. That’s especially if it’s about something like a BMW check engine light that could mean almost anything. It is very easy to misdiagnose this issue and replace a few parts that didn’t need replacing before finding the right culprit for the problem.

Replacing all these components is going to cost you a lot of money in the process. These sensors especially are expensive equipment and can cost more than $300 to replace. If you replace a couple of components, you may end up paying thousands in the process. That’s why you need to learn how to troubleshoot. But how? We are going to teach you.

In this article, we will discuss what is a BMW check engine light. Then, we will give you some instructions on what you should do when you have this issue with your car. We also going to cover all the most probable reasons why this check engine light appears on the dashboard and how you can tackle these problems quickly and effectively. So, let’s discuss.

What Is A Check Engine Light? – BMW Check Engine Light

The check engine light is a visual representation of a problem in your vehicle. This light is located in your cluster. When it turns on, it means that there is some problem with the vehicle. But how does the check engine look like?

The check engine light is usually a picture of a car and a wrench. Or in some cars, only a wrench icon, or perhaps the words ‘check engine’ appears. This icon is usually bright orange and you can easily distinguish it from other icons that are mostly red in color.

So, why this light appears in the first place? As we said, the light appears to indicate a problem with your BMW. The light is displayed by the PCM. And what is a PCM?

The PCM is the powertrain control module. This module is the brain of your car. The PCM is recording the performance of every component and then gives the components the right instructions to work properly.

The PCM is factory programmed computer that knows everything that your car needs to function properly. If some of the components do not deliver the right performance, they start to produce errors. Then, the PCM is receiving these bad data sets from these components. If there are too many of them, the PCM will decide to show the check engine light on the cluster.

Then when you have this information on the dashboard, you know that something is wrong with your car. You don’t know what could go wrong, the BMW check engine light is just there to remind you that you are having a problem and it needs solving as soon as possible. And what should you do when you have this light on your dash? We are going to learn in the next chapter.

What To Do When You Have A BMW Check Engine Light?

This is a good question and we are going to answer it for you. The first thing you should do is not panic. We know that you probably freaked out when you first saw this light, and you don’t know what to do but don’t panic. If you panic, things can only get worse.

If you have a check engine light, there are three options on the table for you. The first and the simplest option is to ignore that there is an issue and pretend that everything is fine. This is the worst option since this problem can turn into something much worse. There could be sufficient damage in your vehicle to deem your car inoperable.

Also, in some of these situations when the problem is not treated, you might end up paying thousands of dollars on repairs because you delayed the repair on this particular problem. So, don’t do this and try to solve the issue.

The second option is to take your car to a BMW service center. There are well-trained technicians that will test your car with original BMW software and troubleshoot your issue. Then they will tell you what is wrong, and how you can fix the problem. This is the best option if you don’t have mechanical knowledge.

And the third option is to troubleshoot the problem by yourself. Troubleshooting the issue on your own will make you learn a lot about cars and you will improve your car knowledge. Troubleshooting is a science by itself and is really easy to do when you start doing it. But how can I troubleshoot? We are going to learn in the next chapter.

What Is An OBD2 Scanner?

Modern cars are filled with computers, sensors, and modules. It’s not like in the old days when everything was analog. To diagnose modern vehicles, you need to have an access to the car computer and that is the PCM.

Since the early 90s, this was standardized and the OBD2 ports were created to ease the diagnosing process. Mechanics now have easy access to the car’s computer.

This OBD2 port is an electronic port that allows connection with a diagnostics device. The OBD2 port is usually located under the steering column. Every car is different and you need to look online to see where is this port located in your car.

BMW Check Engine Light

The next thing you will need is an OBD2 scanner. This scanner basically scans your vehicle for error codes. As we mentioned in the previous chapter, these errors are produced by the PCM to let you know that you have a problem.

These OBD2 scanners could be found for $30 online. When you connect them to the car, they will scan the car and you will get codes if something is wrong with the vehicle. If there are no codes, it means that everything is good.

Then, if you get codes, you need to look for them online and see what do they mean. When you learn these codes, then you can start to test and troubleshoot the problem. And that is getting a multimeter and test the components manually.

This will require some skill. But you shouldn’t worry, there is a ton of information online that you can use to your advantage and get rid of your BMW check engine light.

What Is A Multimeter?

A multimeter is an instrument that is used to measure electrical properties. A basic multimeter can measure resistance, voltage, and electric current. This multimeter is also known as voltmeter or ohmmeter. Since voltmeter is used to measure voltage and resistance, it’s measured in ohms.

There are analog and digital multimeters. Analog multimeters were used in the past, but recently, more advanced digital multimeters have entered the market and deliver many features for a fraction of the price. You can find a multimeter at almost any electrical parts store around the country for $50 or less. This tool is going to be a lifesaver when it comes to troubleshooting.

The multimeter is going to help you troubleshoot numerous sensors and other electrical components that without the multimeter, you can only guess if they are working properly.

By doing this, you will have a clear idea of what is broken in your car and needs replacement. There are a ton of videos online on how you can test a specific sensor on your car and see if it produces the values that it needs. If it doesn’t, you need to replace it with a new one, simple as that.

So, remember, the first thing is connecting the car to an OBD2 scanner and scan for codes. Then, learn the codes and based on these codes start testing the affected components. It cannot be simpler than this.

With these two tools, you are going to save thousands of dollars in the long run. During the ownership of a vehicle, there are a ton of problems that appear. If you solve these problems on your own, you will become a proficient mechanic that can fix the BMW check engine light.

Probable Causes For BMW Check Engine Light

Since we have covered all the troubleshooting basics and we learned what equipment do you need to troubleshoot a BMW check engine light. Now is the right time to discuss which are the probable reasons why this check engine light appears in the first place. We will discuss all the possibilities that can cause this check engine light to turn on. So, let’s begin.

Bad Sensors

A bad sensor is one of the most common reasons why you are getting a BMW check engine light on the dashboard in your BMW. This is the case because the sensors are directly connected with the PCM and the PCM needs the sensors in proper working order to give the engine the right instructions. When these sensors are failing, one of the consequences is this check engine light to appear. What are the sensors that usually go bad? Let’s find out.

O2 Sensor – BMW Check Engine Light

The O2 sensor is one of the most common reasons why you can get a BMW check engine light. This is the case because the O2 sensor is measuring the exhaust gasses. When this sensor is malfunctioning, it means that the computer is receiving the wrong information about the flow of oxygen into the exhaust.

This will result in a check engine light appearing on the dash. This is since the computer is confused and has trouble keeping the engine running properly. This sensor is not cheap and it can cost you between $150 to $350 to replace. This is only for the part. The labor is going to cost you $100 more. Since this sensor is easily accessible, it’s not that difficult to replace.

Mass Airflow Sensor

Similarly, to the O2 sensor, the mass airflow sensor or MAF sensor as its known can fail and cause BMW check engine light to appear on the dash. The good thing about this sensor is that when you get a check engine light, it doesn’t necessarily mean that the sensor is bad. It could only be clogged with debris.

This debris is going to make the sensor malfunction and cause the check engine light to appear. The solution for this is to clean the sensor with an air compressor.

Once cleaned, this sensor should resume working properly again. But if the problem persists, then you know that you will have to replace the sensor with a new one. A new sensor is going to cost you more than $200 and that is for the part only. Luckily, this sensor is easily accessible since it’s mounted on the intake and you can replace it very easily.

Throttle Body Sensor

The throttle body position sensor is also one crucial sensor that can fail and cause the BMW check engine light to appear. This is the case because this sensor is regulating the flap of the throttle body.

The sensor is basically tracking the movement of the flap. If the sensor doesn’t work properly, it can cause your engine to run lean on fuel. This means more air will be sucked while there will be too little fuel. Since the sensor doesn’t know how much the flap has been opened.

This will result in too much air in the engine and very little fuel. Resulting in poor engine work. But luckily for you, this sensor is cheap and easy to replace.

Crankshaft Sensor

The crankshaft sensor is another sensor that plagues a lot of BMWs and infuriates a lot of BMW owners. When this sensor has failed, your car will show the check engine light.

Also, the car will have trouble cranking. When you crank the car, it will need a lot of crank power to get it started. This will affect your battery since this will draw too much power from your engine.

The solution for this problem is replacing the crankshaft sensor with a new one. The best thing is to replace this sensor sooner rather than later. Because if you wait for too long it will completely fail and your car would not start at all.

Ignition Problems

Ignition problems can also attribute BMW check engine light to appear on the cluster. The ignition problems, as we said, appear on components that aid the ignition and spark delivery into the cylinders. So, which are these components? Let’s find out.

Bad Engine Coils

The engine coils are the first in the list of ignition components that can cause a check engine light to appear on the dashboard. What’s the role of these coils? The role of the coils is to deliver the spark from the starter motor to the spark plugs to start the vehicle.

When these coils are bad, they prevent this process and problems may appear. Frequent misfires can happen, or your engine running on one less cylinder than it should.

The coils are extremely important. Fortunately, they can be checked and replaced easily. There are a couple of coils on the engine. One per cylinder. You can easily swap them around to find the faulty one. A new coil is expensive and can cost more than $150 to buy only for the part.

Bad Spark Plugs – BMW Check Engine Light

Bad spark plugs can also cause the check engine light to appear on the dashboard and ruin your day. Although you cannot diagnose them by using an OBD2 scanner, you can try some other methods. And that is similar to the previous example with the coils. You can swap them with other spark plugs and learn which of them are bad.

BMW Check Engine Light

But the best thing is to replace them altogether. I’m saying this because they are extremely cheap and if they weren’t swapped for a long time, the best thing is to get new ones. After you replace them, the BMW check engine light should disappear.

Fuel Delivery Problems

Fuel delivery issues can also cause the check engine light to appear on your BMW. These components are in charge of delivering the proper amount of fuel inside of your cylinders and when the PCM records poor work by some of them, it’s going to show BMW check engine light on the dashboard. Then it’s up to you to troubleshoot. But which are these components, let’s see.

Bad Injectors

The injectors are crucial components for ideal combustion. If the injectors are bad, then there will be a lot of errors and the check engine light will turn on in the cluster.

The injectors are spraying fuel into the cylinder and if they are clogged or they leak too much fuel, then this means that there is something wrong.

The computer will react and will throw a check engine light because of this. Then, it’s up to you to troubleshoot the problem and check the injectors and find out which of them has gone bad.

Fortunately, they are relatively inexpensive. Unless you have a direct injection car or a diesel truck. These injectors cost a lot more to replace.

Bad Fuel Pump

The fuel pump is another key component in the combustion process and without it, the whole process will not work. Since there will be no pressure from the fuel pump. No pressure means check engine light and an inoperable vehicle because there will be so little fuel injected into the engine.

The only solution for this is to test the fuel pump with a multimeter and see if it’s wrong. If the fuel pump is good, the next thing you should check is the fuel filter. If the fuel filter is clogged, it will not allow the fuel to pass. This will result in poor engine work and engine stalling. And BMW check engine light as well. Fortunately, you can troubleshoot the issue and easily find the problem.

Loose Gas Cap

Something simple as a loose gas cap can also cause a check engine light to appear on your dash. So, why is this the case?

This is the case because your gas tank is pressurized. This means that when you tighten up the gas cap. A pressure hose sucks the air and there is no air in the fuel tank.

And if you start your car with the loose gas cap, there will be no pressurization. This lack of pressurization will mean that the BMW check engine light will show on the dash because the system is confused.

Make sure that the gas cap is always tightened up to spec and avoid leaving it loose if you don’t want the check engine light to turn on.

Other Possibilities

There are also other possibilities why check engine light can appear on the dash. These include the PCV valve that is designed to release the pressure. And if it malfunctioned it can cause a BMW check engine light to appear.

Other things that can cause this problem are the EVAP purge valve and the charcoal canister. For example, if the purge valve is open all the time, you most probably will have problems with the check engine light.

BMW Check Engine Light: Facts

  1. A check engine light can appear on your BMW 3-Series, 4-Series, M3, X3, X5, or i3 for a variety of reasons.
  2. Loose or missing gas caps can cause fuel economy and emission issues, triggering the check engine light.
  3. Clogged catalytic converters can severely impact vehicle performance and fuel economy, leading to a check engine light.
  4. Faulty spark plugs or wires can cause engine misfires and reduce fuel economy and performance, causing a check engine light.
  5. A faulty oxygen sensor can cause the engine to receive too much or too little fuel, leading to engine failure or excessive smoke and odor.
  6. The Mass Air Flow (MAF) sensor measures the amount of air entering the engine and helps ensure the proper air-fuel mixture, and a faulty MAF sensor can cause engine misfires and poor fuel economy.
  7. BMW suggests stopping by their service center to diagnose and repair your BMW when the check engine light comes on.
  8. Intermittent check engine lights can be a sign that something is on the verge of failing and should be addressed promptly to prevent the vehicle from not starting again.
  9. Constantly on check engine lights indicate that the onboard diagnostic system has detected a problem that needs to be fixed, even if the vehicle seems to be operating fine.
  10. A blinking check engine light usually indicates a major issue with the vehicle, and the driver should pull over when safe and consider towing the vehicle to a service center.

Conclusion – BMW Check Engine Light

In this article, we have learned a lot when it comes to BMW check engine light and what you can do about this problem when it shows up in your BMW.

We explained the troubleshooting basics and that is an OBD2 scanner tool and a multimeter. Without these tools, you would not be able to do much on these modern cars.

Then, we covered all the possibilities this check engine light can appear. There are more, but these that we mentioned are the most common. And they were the sensor-related issues, fuel injection issues, and fuel delivery problems. There can also be problems with the catalytic converter that can cause the check engine light to appear as well.

The sensor problems are the most prevalent and you should focus on them first before you move to other components.

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1 comment

Sherwin Alvarez 11/07/2021 - 12:31 PM

In many cars, the check engine light indicator can be associated with many factors. However, this indicator can prompt if the battery is getting exhausted. Review your manual and have the battery examined by a professional to confirm if it is functioning in its full ability. If not, you must consider getting a new one.


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