Diesel particulate filter (DPF): how it works, regeneration and costs

A diesel particulate filter (DPF) stops soot particles in the exhaust gases of your diesel car. During regeneration, the collected soot is burned off. Below you can read how it works, what problems can occur and what you can do yourself.

1. How does a particulate filter work?

The DPF sits in the exhaust system of a diesel car. When the engine is running:

1. The diesel engine produces exhaust gases containing soot particles.
2. The exhaust gases flow through the particulate filter.
3. The filter traps a large share of the soot particles.
4. The cleaner exhaust gases leave the car.
5. The trapped soot is regularly burned off during regeneration.

A particulate filter can last for many years if the engine runs well and regenerations can take place regularly.

2. What is regeneration?

Regeneration means the car cleans its particulate filter by raising the temperature inside the filter high enough. There are three types:

• Passive regeneration: during longer journeys with a high enough exhaust temperature.
• Active regeneration: the engine computer automatically raises the exhaust temperature to burn off the soot.
• Forced regeneration: a garage starts a controlled regeneration with diagnostic equipment.

3. How can you tell the car is regenerating?

• The idle speed is sometimes slightly higher.
• Fuel consumption rises temporarily.
• The cooling fan runs harder or keeps running after you stop.
• You may notice a hot or slightly burnt smell.
• The start-stop system may be temporarily switched off.

Not every diesel car shows these signs equally clearly.

4. Why does a particulate filter get clogged?

The most common causes are short trips, frequently interrupted regenerations, problems with the EGR valve, faulty sensors and an engine that produces too much soot.

Even with long journeys, a particulate filter can eventually become clogged. The filter collects not only soot but also ash that does not disappear through regeneration.

5. What to do when the DPF warning light comes on?

With an orange DPF warning, and no other faults or loss of power, a regeneration drive can help:

• Make sure the engine is at operating temperature.
• Drive for about 20 to 30 minutes on a motorway.
• Keep a steady speed, for example 70 to 100 km/h where allowed.
• If possible, keep the engine at around 2,000 to 2,500 rpm, depending on the car.
• Avoid hard acceleration and very high revs.

6. How much does a DPF repair cost?

Indicative amounts, depending on the car and the garage:

• Diagnosis and read-out: €30 to €90
• Forced regeneration: €70 to €180
• Professional cleaning: €200 to €450
• Replacing the differential pressure sensor: €100 to €300
• New particulate filter including fitting: €600 to €2,000 or more

Want to know what your car costs you in total per month, including maintenance and repairs? Work it out with the car cost calculator.