What are Diesel Particulate Filters? How To Avoid DPF Filter Problems?

Every car that runs on diesel fuel is fitted with a diesel particulate filter, and it has been this way for more than the last two decades. Not many people know the function and need for a particulate diesel filter, which has an important function. The particulate filter also needs to be maintained well, and in this blog, we shall look at what a DPF is, what its functions are, and why it needs to be maintained well.

What Is A Diesel Particulate Filter (DPF)?

A Diesel Particulate Filter is a filter that stores the exhaust soot or fumes in a diesel car, which would otherwise be released into the atmosphere.

These came about to reduce the emission and pollution from diesel cars. The capacity of a particulate diesel filter is finite, which means that it needs to be emptied regularly so that it can continue to hold exhaust soot.

If DPFs are not properly maintained, then they could result in engine problems, as a fully loaded DPF causes high back pressure.


What Does A Diesel Particulate Filter Do?

As mentioned earlier, a diesel particulate filter (DPF) holds the exhaust soot of a diesel car. Without this filter, the fumes would be emitted into the environment. They help reduce diesel car emissions, thus helping protect the environment.

The Euro 5 exhaust emissions legislation was introduced in 2009 to help lower car CO2 emissions, which made DPFs mandatory, and since then, around one in two new cars a year have been diesel-powered. In 2018, the UK government made changes to its MOT test requirements, including tougher scrutiny of diesel cars. Properly fitted and working DPFs became one of the necessary requirements and driving a car without a DPF can now result in a £1000 fine.

Why Are Diesel Particulate Filters Important?

The diesel particulate filter of your car is highly important for your car’s health as it traps all the exhaust soot, which would otherwise be emitted into the environment.

It is important for you to ensure that your DPF filter is regularly unblocked so that your DPF remains in the best condition, and so that your car’s overall health is perfect as well.

Neglecting your DPF can result in long term problems, including engine problems.

Also Read: How to Avoid Engine Idling?

How To Tell If Your Diesel Particulate Filter Is Blocked?

If your DPF is full, then you would see an orange light glowing on your dashboard. The symbol for a full DPF is a piped box with dots in between, which you can see below. The design of the DPF symbol might slightly vary from manufacturer to manufacturer.

If you see that the DPF light is glowing, then you would have to take your car out on to an empty road and drive at a speed more than 40 mph, for at least ten minutes, after which your DPF will go into the regeneration mode.

If your DPF light continues to glow even after that, then take it to an expert immediately to fix the problem.

What Causes Your Diesel Particulate Filter To Be Blocked?

One of the main reasons why car manufacturers suggest city folk to opt for a petrol car is because city cars are driven at lower speeds and for a shorter distance. This is because these kinds of journeys, frequently, can result in the blocking of a diesel particulate filter. A diesel particulate filter on a poorly serviced car may fail sooner than a well maintained one. Generally, they should last for at least 100,000 miles.

Using the wrong kind of oil, low quality fuel and performance boosters can all result in the blockage of your DPF.

Apart from that, the following is a list of issues that may affect the proper functioning of your DPF and result in its blockage:

1. Glow Plugs

A Glow plug should never be turned on during the process of regeneration. Ensure your glow plugs are functioning properly as one or more damaged glow plugs can prevent regeneration.

2. Thermostat

A broken thermostat means that your engine will not be able to reach the optimal temperature for the regeneration of DPF.

3. Lambda Sensors

Any damage to the lambda sensor directly affects the results of regeneration. DPF regeneration can also be compromised and can get blocked when the additive tank is empty.

4. DPF Sensors

Any DPF consists of various sensors that track its performance. Thus, any damage to these sensors directly affects your DPF performance and might result in blockage as well.

5. Short Journeys

When you travel for a short distance at low speeds, your engine will not reach its optimal working temperature, which will directly affect the regeneration process of your DPF.

6. Driving At Low Revs

Low revs save a lot of fuel, but they are not good for your DPF regeneration, as the engine takes more time to warm up, and thus cannot regenerate easily.

7. Wrong Engine Oil And EGR Valve Failure

Mid-SAPs and low-SAPs are the right kind of engine oils to be used for cars fitted with DPFs. Also, when the EGR valve is clogged, it may cause the excessive accumulation of soot.

8. Irregular Checks Of Your DPF

Ensure your DPF is checked regularly to make sure that it is not blocked.

How To Avoid DPF Problems?

The most common form of DPF problems is the blockage of DPF. The range of factors that can cause the blockage of your DPF have been discussed above. Apart from that, DPF problems can easily be avoided if you manage to stick to the following tips:

1. Avoid Driving At Low Revs

As mentioned above, driving at low revs will save you fuel, but it will result in the blocking of a particulate filter, so try to avoid driving at low revs at all costs.

2. Drive For Long Distances

For your engine to reach the optimal temperature at which your DPF can regenerate, you need to drive for longer distances.

3. Use The Right Engine Oil

Your engine can be damaged if the wrong engine oil is used. Hence, it is advisable that oils suitable for DPFs should be used.

Also Read: What To Do If You Put The Wrong Fuel In Your Car

4. Get Your Filter Checked

Your DPF filter should be checked at regular intervals for safety. Ensure that you are getting your filter checked at regular intervals.

5. Use A DPF Cleaner

An additive can be used to preventively maintain the particulate filter. An additive facilitates the regeneration of your DPF, thus not causing you any problems.

6. Perform Maintenance On Your Car’s Fuel System

Maintain your car and its fuel system regularly to avoid any sort of DPF related problems.

How Do I Maintain A Diesel Particulate Filter?

The best and only way to ensure the perfect maintenance of your diesel particulate filter is to let it regenerate properly, whenever you see that it is full.

There are two ways to let your DPF regenerate:

1. Active

Active regeneration is when you get a warning that your car’s DPF is full, through the yellow dashboard light. This is when you must make sure that you allow your DPF to regenerate by driving on an empty road for more than 10 minutes, at a speed greater than 40mph.

Not driving for 10 minutes will not let your DPF to fully regenerate, which would result in serious issues, as your DPF would be blocked partially still.

The following is how you will know that your DPF is fully regenerating:

  1. Engine note change
  2. Cooling fans running
  3. A slight increase in fuel consumption
  4. Increase in idle speed
  5. Deactivation of automatic Stop/Start
  6. A hot, acrid smell from the exhaust
2. Passive

Passive regeneration is when the DPF is still not full, and has space left for more exhaust soot to be collected. However, the DPF burns off the collected soot when the car is going at a high speed on long motorways.

Since not every driver goes on such journeys often, active generation is a method that can and should be used whenever necessary.

What To Do If Neither Active Nor Passive Regeneration Work?

Forced regeneration should be opted for, if neither active nor passive regeneration work. Forced regeneration is the process where your DPF is partially cleaned in a garage.

This only clears the excess soot that has been collected and lets your DPF regenerate on its own again. Thus, you would have to either go with the active or passive process of regeneration for your DPF after this.

What Is The Cost Of A New DPF Filter?

A DPF filter price is quite expensive. A new filter for a car from the car manufacturer can cost £1,000 and £3,500. This could result in the wash out of any savings that you may have made with driving a diesel car.

As cars get older, you might encounter DPF problems quite frequently, with the price of a DPF filter going beyond the car’s value even. While some suppliers might be selling DPFs for lower prices, you need to check whether those DPFs are of the right type.

FAQs on Diesel particulate Filter

1. How to fix diesel particulate filter warning light?

Your DPF warning light can be fixed by letting your DPF regenerate. You can do this by letting your DPF burn out the collected soot, by driving for 10 minutes at a speed more than 40 mph.

Also Read: what Are Car Dashboard Warning Lights?

2. Does my car have DPF?

Every diesel car has a DPF, as a DPF reduces emissions into the atmosphere.

3. How to unblock my DPF filter

Clogged DPF filter can be unclogged by taking your car out onto an empty road or motorway and driving it for 10 minutes at a speed more than 40 mph. This helps your DPF burn out all the soot that has been collected within it so far, thus regenerating.

4. How to clean a DPF filter while driving?

Your DPF filter is automatically cleaned while driving, as your DPF automatically burns the accumulated soot during that time.

5. Do I need a diesel particulate filter to pass the MOT?

Yes, your diesel particulate filter needs to pass the MOT, as per the UK government’s new rules set in place in 2018.

6. Is it illegal to remove a diesel particulate filter?

Yes, it is illegal to remove a diesel particulate filter, and you can be fined up to £2,500 for the same.

7. How long should a diesel particulate filter last?

Ideally, your diesel particulate filter should last at least 100,00 miles. If your maintenance is improper, then it would not be able to last for that long.


Car maintenance is important, and something that needs to be done at all costs. Ensuring that your Diesel Particulate Filter is working properly is a part of maintaining your car properly. Failing to maintain your DPF filter and your car will result in long term damages that might end up costing you more than what you paid for your car. An effortless way to maintain your car is giving it regular servicing. Another way is to get a warranty for your car, which will cover all the unexpected repair or replacement costs of your car. Warranty Direct offers a highly comprehensive warranty policy and prioritises customer satisfaction over everything else.

© 2023 – All Rights Reserved