Diesel cars do not perform well in certain situations, such as when used mainly in urban areas and with few kilometers driven on the road. The cause of this problem is the particulate filter, and we will explain why it happens and how to avoid it.
If you have a relatively modern diesel car, there is a component that plays a fundamental role in the operation of the engine and in compliance with anti-pollution regulations: the particulate filter (DPF).
This system, which is also incorporated in some gasoline engines, is key to reducing soot emissions, but it is also one of the parts most prone to failure if not properly maintained.
What is the particulate filter and what is it for?
The particle filter is a device located in the exhaust system that is responsible for retaining the small particles of sootgenerated by the combustion of diesel fuel.
To prevent it from becoming clogged, the car periodically performs a regeneration process, burning these residues at a high temperature.
What is the main problem with the particle filter?
To maintain its efficiency, the particle filter must undergo cycles of regeneration, a process by which the accumulated particles are burned to prevent the filter from becoming blocked.
This procedure takes place without the driver’s knowledge and is divided into two types: passive regeneration and active regeneration.
Passive regeneration
Passive regeneration is a continuous and natural process that takes place without the intervention of the engine management system.
It occurs when the engine reaches sustained high temperatures, as happens when driving on the motorway.
In this context, exhaust gases reach temperatures of between 350 and 500 °C, allowing the soot to oxidize slowly through a reaction with nitrogen dioxide (NO₂), converting it into carbon dioxide (CO₂).
This process is facilitated by the platinum coating on the filter, which acts as a catalyst so that regeneration occurs gradually and efficiently without affecting engine performance or increasing fuel consumption.
Active regeneration
When driving conditions do not allow the temperatures necessary for passive regeneration to be reached, active regeneration comes into play.
In this case, the engine management system takes control and intentionally increases the temperature of the exhaust gases to 600-650 °C, allowing the accumulated soot to burn off.
This process is activated when the DPF sensor detects a saturation of soot above a certain limit. Active regeneration usually lasts around 10 minutes and may require an adjustment in driving to be completed successfully.
In the city, where driving is done at low engine loads and low temperatures, active regeneration is essential to prevent the filter from clogging.
Consequences of incomplete regeneration
If traffic conditions or driving style do not allow active regeneration to be completed, soot will continue to build up in the filter, increasing the risk of severe blockage.
In extreme cases, the DPF can become saturated to the point where automatic regeneration is impossible, requiring a forced cleaning in the workshop or even replacement of the filter.
Furthermore, attempting to regenerate with a filter that is too saturated can raise the temperature to critical levels, putting the integrity of the filter itself at risk.
To avoid this, some vehicles have a warning indicator on the instrument panel, alerting the driver to the need to modify their driving pattern to allow regeneration.
How can I promote regeneration of the DPF?
To avoid problems and extend the useful life of the particulate filter, it is advisable to follow these practices:
- Drive at constant speeds and at medium-high revolutions (legal speed on the motorway in fifth gear is sufficient) for at least 20 minutes on the road or motorway.
- Avoid exclusively urban routes and, if necessary, make periodic trips on the road to promote regeneration.
- Pay attention to the DPF indicator on the instrument panel and act immediately if it flashes, following the instructions in the vehicle manual.
Following these recommendations ensures optimal operation of the particulate filter, reducing the risk of costly breakdowns and ensuring that the diesel engine operates efficiently and ecologically.
A clogged particulate filter will render the vehicle useless.
Problems at the MOT test due to the particle filter
A clogged or tampered particle filter can result in a failure at the Technical Vehicle Inspection (MOT).
Firstly, because there is a risk of a failure indicator appearing on the instrument panel or in the diagnostic OBD.
But, above all, because in emissions tests, if the car emits too much smoke or has abnormally low values (a sign that the filter has been removed), it can be grounds for suspension.
Taking care of the particulate filter is essential to avoid costly breakdowns and problems at the ITV. By following a few simple recommendations, you can extend its life and ensure that your diesel car runs smoothly.
