What is a Diesel Particulate Filter? How To Avoid DPF Filter Problems?

If you own a diesel car, chances are it's equipped with a Diesel Particulate Filter (DPF) in the exhaust system. While these filters have been mandatory in diesel vehicles for two decades, many car owners are unaware of their importance or how to properly maintain them. Neglecting a DPF or tampering with it can lead to costly repairs, decreased performance, and increased harmful emissions.

DPFs play a crucial role in reducing the environmental impact of diesel engines by trapping and burning soot particles. However, to ensure your car runs efficiently and stays within legal emission limits, it’s essential to understand what a DPF is, how it works, and how to keep it in good condition.

In this guide, we'll explore everything you need to know about diesel particulate filters from identifying whether your car has one to maintaining its performance and avoiding potential issues. If you’re concerned about your DPF, consult a trusted garage or mobile mechanic for professional advice.

What is a Diesel Particulate Filter (DPF)?

A Diesel Particulate Filter (DPF) is an essential component of a diesel car's exhaust system designed to capture and store harmful soot produced during fuel combustion. This soot, also known as particulate matter, is a fine substance that can lead to serious health issues such as respiratory problems. Acting as a "soot trap," the DPF plays a crucial role in reducing harmful emissions from diesel vehicles.

What Does a DPF Filter Actually Do?

The primary function of a DPF is to filter out and store the particulate matter generated by diesel engines. By trapping this soot, the DPF significantly reduces the black smoke traditionally associated with diesel vehicles, particularly during acceleration. However, since the filter has a limited capacity, the stored soot must be periodically burned off through a process called regeneration.

Regeneration cleans the filter by burning away excess soot at high temperatures, ensuring the DPF remains effective and prevents blockages that could hinder engine performance. Properly functioning DPFs help diesel vehicles comply with stringent emissions regulations, such as the Euro 5 standard introduced in 2009, which made these filters mandatory in modern diesel cars.

By maintaining the DPF in good condition, you not only improve your car's efficiency but also contribute to a cleaner environment and reduced health risks.

Is It Illegal to Remove a Diesel Particulate Filter (DPF)?

Yes, removing a DPF is illegal in many countries due to the environmental impact it creates. In the UK, for example, car owners caught without a DPF face fines of up to £1,000 for cars and £2,500 for vans. Additionally, removing a DPF can invalidate your car insurance policy and cause the vehicle to fail its MOT test.

Since DPF removal not only increases harmful emissions but also breaks compliance with stringent emissions regulations, it is strongly discouraged.

How Do I Tell If My Diesel Particulate Filter (DPF) Is Blocked?

When your DPF becomes blocked with soot or malfunctions, an orange warning light typically appears on the dashboard. This light often resembles a piped box with dots inside it, although its design may vary by manufacturer. Refer to your vehicle's handbook for specifics on the DPF warning light.

Blocked DPFs can lead to significant engine performance issues. If left unchecked, the blockage can eventually result in engine damage or the car entering "limp-home mode," a state where performance is restricted to prevent further damage.

What Causes a Diesel Particulate Filter (DPF) Blockage?

The primary causes of DPF blockages include:

1. Short Journeys at Low Speeds

Driving short distances without achieving high exhaust temperatures prevents the DPF from regenerating, causing soot to accumulate. This is why diesel cars are often not recommended for city driving or frequent stop-and-go traffic.

2. Poor Servicing

Regular servicing ensures the DPF and engine are running optimally. Neglecting maintenance or using wrong engine oils containing harmful additives can block the filter prematurely.

3. Low-Quality Fuel

Substandard diesel can contribute to quicker soot buildup and filter damage.

4. Running on Low Fuel

Cars running on low fuel levels may avoid DPF regeneration to conserve fuel, leading to clogging.

How to Clean DPF Filter?

Cleaning a Diesel Particulate Filter (DPF) is essential for maintaining your vehicle's performance and ensuring emissions compliance. Here's a step-by-step guide on how to clean DPF filters:

1. Passive Regeneration

• What it is: Passive regeneration happens automatically when the vehicle is driven at high speeds or under a heavy load, allowing the exhaust temperature to reach the necessary levels (above 500°C) to burn off soot particles.
• How to do it:
• Drive on a highway or long stretch at a steady speed (around 40-50 mph) for 30-60 minutes.
• Ensure the engine is fully warmed up before starting.

2. Active Regeneration

• What it is: The vehicle's onboard system initiates active regeneration by injecting fuel to raise exhaust temperatures and burn off soot.
• How to do it:
• Check for the DPF warning light; this indicates a need for regeneration.
• Follow the manufacturer's instructions for active regeneration, which usually involves continuous driving for a specific duration.

3. Forced Regeneration (Professional Service)

• What it is: A mechanic uses specialized equipment to clean the DPF by forcing high temperatures to burn off accumulated soot.
• How to do it:
• Visit a workshop or authorized dealer.
• A diagnostic tool is connected to the vehicle to trigger the forced regeneration process.
• This process is ideal when the DPF is heavily clogged.

4. Cleaning with Additives

• What it is: Fuel additives designed to reduce soot accumulation can help in regular maintenance.
• How to do it:
• Purchase a DPF cleaner additive compatible with your vehicle.
• Mix it with the fuel according to the instructions on the product.
• Drive for the recommended distance or time for the additive to take effect.

5. Manual Cleaning (For Severely Clogged DPFs)

• What it is: Physical cleaning involves removing the DPF and manually cleaning it.
• How to do it:
• Step 1: Remove the DPF from the vehicle (refer to the vehicle's service manual for instructions).
• Step 2: Use a high-pressure air or water jet to dislodge the soot and ash.
• Step 3: Dry the filter thoroughly before reinstalling.
• Alternatively, take it to a professional who specializes in DPF cleaning using ultrasonic or chemical cleaning.

6. Avoiding Future Problems

• Preventative measures:
• Use low-sulphur diesel fuel.
• Regularly check for and clear engine fault codes.
• Avoid excessive idling, as it leads to soot buildup.

When to Replace the DPF?

If cleaning does not resolve the issue or the filter has reached the end of its service life, replacement may be necessary. Always consult your vehicle's manual and a professional mechanic for specific advice related to your vehicle's DPF system.

How Do I Maintain a DPF Filter?

Proper maintenance of a diesel particulate filter (DPF) is essential to keep it functioning efficiently and to avoid expensive repairs. Here are some practical tips for maintaining your DPF filter:

1. Enable Regular Regeneration:

a. Passive regeneration occurs naturally during long, high-speed drives (e.g., on motorways or highways). Ensure you take your car for a 30–50-minute drive at speeds above 40 mph regularly.

b. Active regeneration occurs during shorter drives when the car's ECU injects extra fuel to burn off soot. If you notice the warning light, drive at higher speeds for at least 10–15 minutes to complete the process.

2. Use High-Quality Fuel:

a. Low-quality diesel can contribute to soot buildup. Stick to premium fuel options that promote cleaner combustion.

3. Avoid Frequent Short Trips:

a. If you primarily make short trips, the exhaust system doesn't get hot enough to burn off the soot, leading to blockages. Combine short trips into longer ones where possible.

4. Use the Correct Engine Oil:

a. Always use engine oil recommended for diesel engines with DPFs. Some oils have additives that can clog the filter.

5. Schedule Regular Servicing:

a. Follow your vehicle's maintenance schedule to ensure all components, including the DPF, are in good condition.

6. Keep an Eye on DPF Warning Signs:

a. If the DPF warning light appears, act promptly by completing a regeneration cycle or seeking professional help if necessary.

What Happens if DPF Regeneration Fails?

If passive or active regeneration doesn't resolve the DPF warning light, a blocked filter may require professional cleaning through a process known as forced regeneration.

Forced regeneration involves using specialized equipment to clean the filter and costs around £100. While it's not always guaranteed to work, it often restores the DPF's ability to regenerate automatically. However, if ignored, the issue may escalate, leading to expensive DPF replacement costs ranging between £1,000 and £3,500.

How Long Should a DPF Last?

With proper maintenance and driving habits, a DPF can last up to 100,000 miles. Regular servicing, using high-quality fuel, and ensuring timely regeneration cycles are key to extending its lifespan.

When purchasing a used diesel vehicle, always check MOT and service records to avoid unexpected DPF repair costs.

Do I Need a Diesel Particulate Filter (DPF) to Pass the MOT?

Yes, a DPF is mandatory for passing an MOT test. Since 2014, MOT checks include verifying the presence and functionality of a DPF. If the DPF is removed or the dashboard warning light remains on, the car will fail the test.

FAQs About Diesel Particulate Filters

1. Is it OK to drive with the DPF light on?

It is not advisable to ignore a glowing DPF light. While it may indicate a partially clogged filter, continuing to drive without addressing it can worsen the blockage and potentially cause engine damage. Taking a long drive at sustained speeds can often help the DPF regenerate, but if the light persists, consult a mechanic immediately.

2. How do you clear a DPF?

DPFs can be cleared through passive or active regeneration:

• Passive regeneration: Occurs naturally during long, high-speed drives, such as on motorways, as the exhaust temperature burns off excess soot.
• Active regeneration: The car's engine management system injects extra fuel to raise exhaust temperatures and burn the soot.

If these methods fail, a forced regeneration performed by a mechanic may be required.

3. What happens when the DPF is blocked?

A blocked DPF can cause:

• Reduced engine performance
• Increased fuel consumption
• Engine warning lights turning on
• Your vehicle entering "limp-home mode" or even failing to restart

To avoid costly repairs, address any DPF-related warning signs promptly.

4. Why does my diesel particulate filter light keep coming on?

The DPF light typically indicates a partially or fully clogged filter. Common causes include:

• Frequent short journeys where the DPF cannot regenerate
• Poor-quality fuel or engine oil
• Poor vehicle maintenance

Addressing these issues promptly can help prevent further complications.

5. How much does a DPF cost?

The cost of a new DPF can range between £1,000 and £3,500, depending on the car's make and model. Older vehicles might even have DPF replacement costs exceeding the car's value. Cheaper aftermarket options are available but must meet Type Approval standards.

6. How long does it take to clear a diesel particulate filter?

Regeneration can take anywhere from 10 to 50 minutes, depending on the method:

• A passive regeneration may require a sustained motorway drive of 30–50 minutes.
• An active regeneration can typically clear the filter in about 10–15 minutes if conditions are right.

7. Can I clean a DPF myself?

Cleaning a DPF yourself is possible using DPF cleaning products or additives available in the market, but it requires careful handling. However, for more severe blockages, professional cleaning or forced regeneration by a garage is recommended to avoid causing further damage.

Conclusion:

The Diesel Particulate Filter (DPF) is essential for reducing harmful emissions in diesel vehicles, improving air quality, and maintaining engine performance. Proper maintenance, such as regular cleaning and avoiding short trips, can help prevent costly repairs and engine damage. If issues persist, professional help may be needed for forced regeneration or filter replacement. Additionally, using high-quality fuel and servicing your vehicle regularly can extend the lifespan of your DPF. To avoid unexpected repair costs, consider a warranty that covers DPF-related repairs. Warranty Direct UK offers comprehensive coverage for diesel vehicles, ensuring peace of mind and optimal vehicle performance.