7 Serious Symptoms Of A Blocked DPF Filter (Diesel Problems)

Are you suspecting that your DPF filter is blocked, and you are interested in learning more about the symptoms of a blocked DPF filter? Well, if that is the case, you are at the right place.

In this article, we are going to elaborate on the symptoms of a blocked diesel particulate filter in great detail, and we’ll also show you how to fix this issue and how much it costs to do so.

Let’s get into it with the basics!

What is a DPF Filter on Diesel Vehicles?

But first, let’s learn what a DPF is and what it does in a car. DPF is an abbreviation for Diesel Particulate Filter. In other words, this is a special filter that is present in diesel vehicles only.

What the DPF does is, it collects the carbon particles that are created in the combustion process of a diesel vehicle and prevents them from escaping into the atmosphere. The DPF is a pretty crucial device when it comes to tackling emissions.

And another important thing when it comes to DPFs is their regeneration. The regeneration is a process when the DPF is cleaning out these captured carbon particles by essentially burning them out. This is a process that occurs at highway speeds and at higher RPM. This process is essential to prevent the DPF from blocking. If you don’t do this, you will end up with a blocked DPF.

We also wrote a detailed guide on how to drive and maintain a diesel car to prevent engine problems, including DPF problems.

So, the chance to find one of these filters in gas-powered cars is 0%. This DPF filter comes as standard on every new diesel engine whether this is a car, pickup truck, semi-truck, or a similar vehicle.

Symptoms of a Blocked DPF Filter

Now that, we covered the basics of the DPF filter and learned more about the operation of this component. We can now move on and discuss the symptoms associated with this component and learn what type of symptoms the DPF makes when it is going bad.

Common symptoms of a blocked DPF filter include:

  • DPF Warning light ignition
  • Low engine power and limp mode
  • Engine stalls and hard start-up
  • Reduced fuel economy
  • Black exhaust smoke
  • Smell of burnt diesel
  • Turbocharger failure

1. DPF Light Turned On

The first thing that you will notice when your DPF is not functioning right is the DPF light that will turn on. Many cars have this dashboard warning light and this is usually an icon with DPF filter, indicating that it’s clogged and needs to be regenerated.

When this light turns on, you need to drive the car on the highway and this will hopefully remove this light. In other words, the DPF will unclog itself.

This happens because the DPF has to work at certain temperatures in order to clean itself. If you do a lot of city driving, you will not make the DPF reach operating temperature and start to regenerate. In this case, the DPF will completely clog up and fail if you are unaware of this.

Some cars unfortunately do not have this light and they will turn on the check engine light when you have DPF issues, especially with the DPF pressure sensor.

The check engine light usually turns on when the DPF is completely obstructed and does not allow the gasses to run out from the engine.

In order to diagnose a check engine light, you need to get yourself an OBD2 scanner to get access to these codes. This can be challenging for beginners. But luckily these tools are pretty cheap and will only set you back $30 to $70.

The good thing will be that you will be able to diagnose every trouble code with this tool. This is why we recommend getting one.

2. Low Engine Power (Limp Mode)

Another very common symptom of a blocked DPF filter is the situation when you experience low engine power. In other words limp mode. This is the situation when you get barely enough power to move your car to your home. 

When the car limps, it is stuck working at low RPM and also at a low speed of 20 mph or less in some cases. This is why it is called limp mode.

Whenever you experience limp mode, you will have trouble revving the car and until you solve the problem or clear the check engine light, this will be the case.

But even if you clear the check engine light, the check engine light will return and again you will experience problems and limp mode.

The only way around this problem if this is indeed caused by a clogged DPF is to remove the DPF from the car or truck and pressure wash it. There are many services out there that are offering to clean a DPF. And with the wider introduction of these filters, the need to clean the blocked DPF filter is more and more common.

3. Trouble Starting/Engine Stalls

Trouble starting and frequent engine stalls will be other very common symptoms when you have a blocked DPF filter. So, why is this the case?

Well, this is the case because your engine releases gasses, these gasses have to go somewhere. And this way is through the DPF. So, when the DPF is blocked, these gasses will create an obstruction.

This situation is known as backpressure. In other words, the gasses that are released from the exhaust are working as an air brake.

This will prevent the engine from building up the boost and delivering power. Resulting in trouble starting the engine and stalling the engine in some extreme cases when the DPF is too obstructed.

In these situations, the only way around this problem will be manual removal of the DPF and cleaning the DPF with high-pressure water.

Only by doing this, you will be able to remove the soot from the DPF and resume normal driving. If not, the car/truck will be pretty much undrivable and the engine will have constant running issues.

4. Reduced Fuel Economy

Poor fuel economy can also be attributed to this problem. So, why is this the case, how will fuel economy suffer in these situations?

In some cases, the DPF can be blocked completely and the enormous pressure will simply destroy the filter. This situation will allow more air to pass through and the more air, the more fuel will be injected into the engine.

This will result in great performance improvement but the car will pollute a lot and also it will waste a lot more diesel. The fuel economy might drop to more than 3L per 100km or even more in some cases.

Another bad thing is that if you live in a country where there are tight regulations when it comes to emissions like Germany for example, you will not be able to pass the TUF inspection.

They will fail your car and will tell you that you need to replace the DPF in order to pass and register the vehicle. This is understandable because without a DPF a diesel vehicle pollutes a lot more compared to a car with a properly working DPF.

5. Black Smoke From Exhaust

Another symptom whenever there is a problem with the DPF, more notably when the DPF is blocked and then damaged, is the case when you experience black smoke.

When diesel burns, it doesn’t burn clean like gasoline. It creates a big amount of soot. This is the case because diesel is generally more oily and energy-dense fuel compared to gasoline.

And whenever you run diesel with a bad DPF, there will be clouds of smoke coming from the exhaust pipe.

This smoke will be very notable especially when you run the car at relatively higher RPM. So, if you press on the throttle, you will get an instant cloud of smoke behind you.

And this is bad. The car will pollute a lot more and you will also risk the chance of being pulled over by the police and sent to the technical station in order to get your car inspected for emissions. In this case, you will be obliged to pay a fine and also fix the problem with your blocked DPF filter.

6. Smell Of Burnt Diesel

The smell of burnt diesel is also very common when the DPF is blocked. This is the case because whenever there is blockage of the DPF, the exhaust manifold gasket can fail.

This will cause an exhaust leak to develop and you will start to experience the smell of fumes inside of the cabin.

You definitely don’t want to breathe these toxic fumes. This is why if you notice something like this, react quickly and avoid further health hazards.

Breathing these gasses can lead to many respiratory problems down the line. This is why if you notice this symptom of a blocked DPF filter, the important thing is to react quickly.

7. Turbo Failure

And the last symptom of a blocked DPF filter is the situation when you have a turbo failure. So, why does this happen, how can a turbo fail because of this problem?

The answer is simple, too much backpressure. Backpressure will destroy your turbo much sooner compared to the case when you have less backpressure.

In addition to this, another big factor that will destroy the turbo is the high heat. The hot side of the turbo will be much hotter than it normally should.

In this case, the turbo will overheat and will simply fail. This is why we definitely recommend that you address the problem before the blockage damages your turbo since even a rebuild on your turbine will cost you a lot of money.

What Happens If The DPF Filter Is Blocked?

Whenever the DPF filter is blocked, you could experience a variety of different symptoms. Most notably, the DPF light will tell you that the DPF needs to regenerate.

When this light is turned on, you will have to take your car on the highway and drive the vehicle at higher speeds in order to clear the soot from the DPF.

Unfortunately, if there is too much soot, this will not help and the filter will not like to regenerate. The only way around this problem would be to completely replace the DPF with a new one or take the DPF and clean it.

There are many services that offer this type of cleaning nowadays and it is completely normal to do it. Since cleaning the DPF is a lot cheaper compared to completely replacing the component.

Other symptoms that will be present when the DPF is blocked will be the check engine light, engine stall, difficulty starting, low engine power (limp mode), gas fumes inside of the cabin, and also turbo failure in the worst-case scenario.

This is why it is really important that you address the problem before it gets too late and the DPF ends up completely blocked.

How To Check And Tell If Your DPF Is Blocked?

There are a number of symptoms that will indicate that you have a problem with a blockage of your DPF.

The first symptom is the DPF light that will turn on to indicate that you need to regenerate your DPF filter. In addition to this, if the filter is too clogged, the engine will also go into limp mode. In other words, it will only deliver limited power.

Also, there can be difficulty starting, engine stalling, gas fumes into the cabin, and in some instances, the turbo can also fail.

In more extreme cases, you will also get the check engine light and there will be some codes that will indicate that the DPF is not performing well.

But the only way to check this DPF filter is to simply remove it from the car. This can be expensive since the DPF is mounted below the vehicle and you will highly likely not be able to do it in home conditions.

So, visiting a shop for this job is the smartest thing that you can do. It might be on the expensive side but it is the only way if you don’t have the proper equipment to remove the DPF.

Can A Blocked DPF Cause Limp Mode?

Yes, a blocked DPF will cause the car to go into limp mode. Why is this the case? This is the case because the car is smart enough to warn you and tell you that you have an obstruction in the exhaust and this problem needs solving. Since if you don’t solve the problem you will end up with an even bigger problem like turbine failure.

We recommend that you visit the shop once the check engine light and limp mode are active. In some cases, this can be simply triggered by the DPF sensor. That’s why proper diagnostics is essential when it comes to these issues.

Can A Blocked DPF Cause Overheating?

Yes, a blocked DPF filter can cause the engine and its components to overheat. But even more common than the overheating of the engine here, the component that can overheat is the turbo.

Let’s say that the DPF is obstructed, in this case, you will have a lot of hot gasses on the hot side of the turbo. And this heat will be constant on this side. This will result in turbo overheating and turbine failure. This problem will not happen all of a sudden.

But if you run the car like this for a few thousand miles, this would be one of the outcomes. In the end, you will pay for a new turbo and a new DPF. This is why proper diagnostics on time is essential to avoid these problems.

Can A Blocked DPF Damage Turbo?

Yes, a blocked DPF can damage the turbocharger. Not immediately, but running the engine like this for a few thousand miles will result in turbo damage. Why is this the case?

There will be too much heat on the hot side of the turbo. As we all know the turbo is cooled and lubricated with engine oil. If the hot side is too hot, this will result in the engine oil cooking off. And this will blow the bearings and other seals that are located in the shaft of the turbo. Resulting in a complete turbo failure.

This is why we recommend that you address the problem with the blocked DPF filter before the issue damages the turbocharger.

Will DPF Clog If The EGR Is Clogged Or Blocked?

Yes, a bad EGR will affect the DPF and will block the DPF much sooner than anticipated. Why is this the case?

This is the case because the faulty EGR will increase the amount of particles that are released and this will cause the DPF to be blocked sooner. These two components are closely connected and the work of the one greatly affects the other in the process. So, it is really important that you react quickly before the problem with the EGR ruins the DPF.


The problem of a blocked DPF filter is a serious issue that shouldn’t be ignored. The DPF is a pretty crucial component in every modern diesel engine and if this component is not in the best shape, you will highly likely fail the emissions testing and eventually damage your engine.

If you own a modern diesel car, you might also want to read our guide on AdBlue problems.

In order to know when this component is obstructed, you have to rely on the symptoms that the DPF makes, which are the DPF light on the cluster, check engine light and limp mode, poor engine performance, and poor fuel economy.

The only way around this problem is to remove the DPF and clean the DPF with a special machine. Luckily, there are many services that offer this and you should definitely consider it before you decide to replace it. Since a new unit is much more expensive than simply cleaning the DPF.

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