How DPF regeneration works
The DPF catches soot from diesel exhaust. The filter has limited space, so the soot has to be burned off from time to time. This burning is called regeneration. A little ash is left over from the soot, and regeneration cannot remove ash.
- By itself, on the open roadWhen you drive for a long time on a motorway or fast road, the exhaust is hot enough for the soot to burn off by itself. You don't notice anything.
- The computer starts it when the filter fills upA sensor tells the engine computer how full the filter is. The computer then injects a little more fuel to make the exhaust hotter. On many cars this happens roughly every 500 km and takes 5 to 10 minutes of driving.
Forced regeneration with a diagnostic toolWhen the filter is too full to clean itself while driving, we start a regeneration through the car's computer with a diagnostic tool.
When the DPF light is on
The light means the filter has filled with soot or there is a fault in the filter system. Driving then usually cleans the filter, without stopping.
How long and how fast to drive depends on the car
- Most often: about 10 minutes faster than 65 km/h.
- Some cars: 15 minutes at 70 km/h or more.
- Some cars: 25 minutes above 60 km/h.
- The exact procedure is in the car's manual.
If the light doesn't go off after such a drive, turns red, flashes or the engine light comes on too, don't wait. A filter that is filling up can be fully blocked soon after.
A blocked filter is protected by the car cutting engine power, and then even fast driving no longer helps. The sooner the filter is cleaned by regeneration, the smaller the chance it has to be replaced. More about car diagnostics
How to tell that a regeneration is running
While the computer is cleaning the filter, you will notice some of these:
- the engine sounds different from usual
- the fans under the bonnet are running
- the engine idles at higher revs
- start-stop doesn't switch the engine off
- a hot, acrid smell comes from the exhaust
- the car uses a little more fuel
If you can, don't switch the car off then. When the drive is cut short, the regeneration doesn't finish and the light stays on. More about why start-stop doesn't switch the engine off
Why the filter fills up and regeneration doesn't work
- You only drive short distances in townThe engine and exhaust don't get hot enough, and the regeneration doesn't have time to finish. This is the most common reason for a blocked filter.
- There is little fuel in the tankOn many cars regeneration doesn't start when the tank is less than a quarter full.
The oil isn't the one the manufacturer specifiesA diesel with a DPF usually needs low-ash oil. The wrong oil blocks the filter sooner.
A fault in the injection, the EGR valve or the filter sensorThe engine then makes more soot than the filter can burn off, or the computer doesn't know how full the filter is.- The computer has stored a faultA stored fault can prevent regeneration until it is repaired.
- On some Peugeots and Citroëns, the additive has run outThese cars have a separate tank with a fluid that mixes with the fuel and helps the soot burn. When the fluid runs out, the filter blocks quickly.
That is why after a forced regeneration we always look for the cause as well. If the cause remains, the filter fills up again.
How to make the DPF last longer
A well-maintained DPF often lasts more than 160,000 km, sometimes as long as the car. Do not drive for long with the DPF light on: the sooner the filter is cleaned, the smaller the chance of damage.
Forced regeneration, cleaning or replacing the DPF
When too much ash has built up, even a forced regeneration no longer cleans the filter. It is then removed and cleaned with a special process, or replaced with a new one. More about DPF cleaning
