Why Is My Check Engine Light On Volkswagen? (11 Reasons Why)

Nothing alarms drivers more than the check engine light suddenly flashing. After all, check engine lights are there to signal you to a host of possible problems going on in your car.

If you are a Volkswagen owner who has never encountered this before, do not panic. There are several reasons—most of which are not serious—for this, and we will list them all here!

Why Is My Check Engine Light On Volkswagen?

Your Volkswagens’ check engine light can be triggered by something as simple as a loose fuel cap. Or, it can be a sign that there’s something seriously wrong in your car, like your oxygen sensor and mass airflow sensor failing. Your spark plugs and their wires could be worn, or your catalytic converter might malfunction.

If you are interested in learning more about the most basic and the most alarming reasons your Volkswagen’s check engine light is on, keep on reading!

1. Your Oxygen Sensor Is Failing

Your car’s oxygen sensor is responsible for measuring the amount of oxygen in your car’s exhaust system that has not been burnt.

Through the O2 sensor, your car’s computer can adjust the amount of fuel and air mixture that goes into the cylinders. When an O2 sensor malfunctions, your car burns more fuel.

As such, your check engine light will turn on to tell you that your oxygen sensor either needs to be repaired or replaced entirely for your car to maintain a good fuel economy.

2. Your Mass Airflow Sensor Is Declining

Through your car’s mass airflow (MAF) sensor, the amount of air entering your engine is monitored, and your car can easily adjust to altitude changes.

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Apart from the check engine light turning on, you will know if your MAF sensor needs checking when your engine has trouble starting, and your mileage is reduced.

3. You Have A Loose Fuel Cap

While a loose fuel cap seems like a trivial matter, it will trigger the check engine light. Mainly, this is because a loose fuel cap can leak gasoline fumes and affect the system’s pressure.

Usually, check engine lights will turn on due to loose fuel caps after you fill up. However, should this be a frequent problem, it may be time to replace the fuel cap altogether.

4. Your Catalytic Converter Is Malfunctioning

Catalytic converters are responsible for turning the carbon monoxide produced by your car into carbon dioxide. As a result, your car will be sluggish and have a rotten smell.

Additionally, a catalytic converter malfunctioning is bad news, mainly because replacing it costs upwards of $200.

For these reasons, your check engine light will flash and prompt you to have your catalytic converter diagnosed and repaired as soon as possible.

5. Your Spark Plug & Ignition Coil Have Problems

Problematic ignition coils and spark plugs spell a lot of trouble for you and your car. You will know if this is the case because of symptoms like engine misfire and difficulty accelerating.

Worse, worn or malfunctioning ignition coils and spark plugs can eventually cause your car to seize up.

Therefore, to prevent this, your check engine light will turn on at the first sign of trouble.

6. Your Spark Plugs Have Bad Wires

Your Spark Plugs Have Bad Wires

It is not only your spark plug that can have issues. spark plug wires can also experience problems while transferring electricity from the ignition coil to the spark plug.

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Further, some of the most common signs of bad spark plug wires are reduced gas mileage, rough idle, and a considerable drop in your engine’s overall performance.

As soon as your check engine light turns on, getting your spark plug wires checked should be your top priority.

7. Your Aftermarket Alarm Is Not Installed Properly

Whenever an aftermarket alarm is not installed properly, you will encounter troubles like drained batteries and engines that will not start.

Most alarmingly, your aftermarket alarm will be triggered by almost anything, from a brush of a finger to a fallen leaf.

Therefore, to spare you from the trouble that comes with a faulty aftermarket alarm, your check engine light will flash and get you to have your car diagnosed.

8. You Have A Vacuum Leak

Vacuum hoses can deteriorate with age. That said, you will notice that the hoses will be cracked and dry over time and with too much exposure to fluctuating temperatures.

Additionally, loose connections and cracked fittings can cause your vacuum hoses to lose their integrity.

As such, your check engine light will turn on to encourage you to check your vacuum hoses for leaks and related problems.

9. Your Exhaust Gas Recirculation Valve Is Failing

One of the components that allows your car to run smoothly is the exhaust gas recirculation system (EGR). It does this by lowering your engine’s nitrogen oxide output.

However, the EGR valve can get clogged over time. When neglected, the EGR can fail completely and require a visit to a reputable mechanic.

Therefore, this is why you must always check your car’s EGR valve whenever the check engine light turns on.

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10. You Have A Dead Battery

Naturally, a dead battery will not even allow your car to start. At this point, you can either charge or replace your battery or get a mechanic to do the job for you.

Fortunately, dealing with a dead battery is simpler than it sounds, especially if you have a newer Volkswagen model.

Seeing as a dead battery is a grave problem for drivers, the check engine light will warn you beforehand when something is going wrong with your battery.

11. Your Check Engine Light Gave A False Alarm

Like all other components of your car, your check engine light might simply be malfunctioning.

So, if you have checked every part of your car and your mechanic has confirmed that everything is in good condition, it may be that your check engine light gave a false alarm.

To know more, you can also read our posts on why your truck smokes when you start it, why your car is stuck in park, and why your car is honking by itself.


Check engine lights are useful in determining existing and burgeoning problems in your car’s engine and exhaust system.

However, the check engine light does not specify what exactly is causing it to go off. As such, you have to diagnose your car from top to bottom to get an answer.

Often, the check engine light turns on for something as simple as a loose fuel cap, and sometimes it is triggered by something more severe like a vacuum leak.

Regardless, heeding your check engine should spare you from troublesome and expensive car repairs in the future.

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