Diesel Particulate Filter (DPF): What It Is and How to Maintain It
Car Owl
Published in English •
Summary
- What it does: Captures soot particles from diesel exhaust to reduce emissions.
- Regeneration: The DPF needs to burn off accumulated soot, which requires regular longer drives.
- Warning signs: DPF warning light, loss of power, increased fuel consumption.
- Avoid short trips: If you only do short journeys, a diesel may not be the right choice.
If you drive a diesel car, you have a Diesel Particulate Filter. It's a crucial part of your exhaust system that traps harmful soot - but it needs looking after.
This guide explains how DPFs work, how to maintain them, and what to do if problems occur.
What Is a DPF?
A Diesel Particulate Filter is a component in the exhaust system of diesel vehicles. It captures and stores soot (particulate matter) that would otherwise be released into the atmosphere.
DPFs have been mandatory on diesel cars since 2009 (Euro 5 standards). They reduce particulate emissions by around 80%.
How Does a DPF Work?
The DPF captures soot particles as exhaust gases pass through it. Over time, the filter fills up with soot and needs to be cleaned - a process called "regeneration."
Regeneration Types
| Type | How It Works |
|---|---|
| Passive regeneration | Happens automatically on motorway/A-road driving when exhaust temps are high enough (400°C+) |
| Active regeneration | The car injects extra fuel to raise exhaust temperature. Takes 10-20 minutes. |
| Forced regeneration | Done by a garage using diagnostic equipment if normal regeneration fails |
Why Do DPFs Get Blocked?
The most common cause is driving patterns. DPFs need heat to regenerate, and short trips don't generate enough heat.
Risk Factors
- Short journeys: City driving, school runs, local trips
- Stop-start traffic: Exhaust never gets hot enough
- Low-quality fuel: Creates more soot
- Wrong oil: Non-low-ash oil can clog the filter
- Faulty sensors: Engine management issues can prevent regeneration
- Ignoring the warning light: The longer you leave it, the worse it gets
Key point: If you mainly do short urban trips, a diesel car may not be suitable. Consider a petrol or hybrid instead.
Warning Signs of DPF Problems
- DPF warning light: An orange light on your dashboard (often looks like a rectangle with dots)
- Loss of power: The car may enter "limp mode"
- Increased fuel consumption: Failed regeneration attempts use more fuel
- Rough running: Engine may feel lumpy or hesitant
- Strong exhaust smell: Particularly when regeneration is attempted
If you see the DPF warning light, don't ignore it. See below for what to do.
What to Do If the DPF Light Comes On
- Don't panic or stop immediately
- Find a road where you can drive at 40-60mph for 15-20 minutes
- Keep the revs above 2,000 RPM (use a lower gear if needed)
- This allows the DPF to regenerate
- The light should go off once regeneration is complete
If the light stays on, or comes on frequently, book a garage appointment. Don't keep driving and ignoring it.
How to Keep Your DPF Healthy
1. Take Regular Longer Drives
Aim for at least one 20-30 minute motorway/A-road journey per week. This allows passive regeneration to occur naturally.
2. Use the Right Oil
DPF-equipped vehicles need "low-SAPS" oil (low in Sulphated Ash, Phosphorus, and Sulphur). Check your handbook and use the correct specification.
3. Use Quality Fuel
Premium diesel can contain additives that reduce soot production. Consider using it occasionally.
4. Don't Interrupt Regeneration
If you notice the fan running after stopping, or a slightly burning smell, your car may be mid-regeneration. Let it finish if safe to do so.
5. Keep the Car Serviced
Regular servicing ensures sensors and engine management systems work properly, which helps regeneration.
DPF Cleaning and Repair Costs
| Service | Typical Cost |
|---|---|
| Forced regeneration (garage) | £100-200 |
| Chemical cleaning | £200-400 |
| Professional DPF clean | £300-600 |
| DPF replacement | £1,000-3,500+ |
Prevention is much cheaper than cure. Maintain your DPF properly to avoid these bills.
Is DPF Removal Legal?
No. Removing or tampering with a DPF is illegal in the UK.
- It's an MOT failure (checked since 2014)
- Fines up to £1,000 for cars, £2,500 for vans
- Garages that remove DPFs can be fined up to £5,000
- Your car won't meet emissions standards
For more on MOT requirements, see our guide.
Should You Buy a Diesel?
Diesels with DPFs are best suited to:
- Drivers who cover high mileage
- Regular motorway or A-road driving
- Those who drive 10,000+ miles per year
If you mainly do short urban trips, a petrol, hybrid, or electric car is a better choice. For more, see our petrol vs diesel guide.
Common Questions
How often should regeneration happen?
Typically every 300-500 miles, depending on driving style. You may not notice it happening.
Can I add DPF cleaning additives to my fuel?
Yes, some fuel additives claim to help burn off soot at lower temperatures. They can help but aren't a substitute for proper driving patterns.
Will a blocked DPF damage my engine?
If ignored, yes. Exhaust backpressure can cause engine damage. Address DPF issues promptly.
Final Thoughts
Your DPF is essential for reducing harmful emissions, but it needs the right conditions to work properly. If you drive a diesel, make sure you take regular longer journeys at higher speeds.
Ignore the warning signs and you could face a repair bill of thousands. Look after your DPF and it will look after you.
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