If you own a modern diesel car, it is probably equipped with an FAP. This component, key in the reduction of pollutant emissions, is often unknown to many drivers… until it gives problems.
At Oxyhtech we explain what the FAP car is, how it works, why it is so important to keep it in good condition, what symptoms alert you to a breakdown and what solutions exist to clean or repair it without having to replace it with a new one.
What is the FAP or particulate filter?
The FAP (Particulate Filter) is a device integrated in the exhaust system of diesel vehicles. Its function is to capture solid particles (soot) generated during combustion, preventing them from escaping into the environment.
In some countries it is known as DPF (Diesel Particulate Filter). Both terms refer to the same system.
Importance of the DPF in diesel cars
The FAP was born as a response to European environmental regulations. From Euro 5 onwards, all new diesel vehicles must have it as standard. Its purpose is to reduce air pollution caused by fine particulate matter, which directly affects health.
Without FAP, a modern diesel car would emit up to 100 times more solid particles.
How the FAP works
Filtering process
The FAP consists of a porous ceramic structure. When exhaust gases pass through the filter, solid particles are retained in its internal channels.
Over time, the filter fills up and needs to be cleaned to prevent clogging.
Filter regeneration
Regeneration is the process by which the FAP automatically burns off accumulated soot.
There are three types:
- Passive regeneration: occurs during long journeys, with a warm engine.
- Active regeneration: the car injects extra fuel to raise the temperature and burn the soot.
- Forced regeneration: it is carried out in a workshop with diagnostic equipment when the previous ones fail.
Why is the FAP important?
Environmental benefits
- Reduces PM10 and PM2.5 particulate emissions.
- Improves air quality in the city.
- Meets CO₂ and NOx emission reduction targets.
Regulatory compliance
Driving with a faulty or cancelled FAP is illegal in Spain. In addition to polluting more, the vehicle does not pass the ITV and can be sanctioned with significant fines.
Location of the FAP in the car
The FAP is integrated in the exhaust line, just before or after the catalytic converter, depending on the design of the vehicle. It is usually a medium-sized cylindrical metal part, located under the car.
In some models it is attached to the catalytic converter forming a single unit (FAP + CAT).
Symptoms of FAP failure
Common warning signs
- Engine malfunction light on.
- Loss of power or uneven acceleration.
- Increased fuel consumption.
- Very frequent or failed regenerations.
- Fan that does not shut off after stopping the engine.
- Excessive or dark-colored smoke from the exhaust.
Consequences of a clogged FAP
- Saturation of the exhaust system.
- Damage to the turbo due to excessive back pressure.
- EGR valve failure.
- Possible activation of the emergency mode (power limitation).
- Risk of engine breakdown if not acted upon in time.
Maintenance and cleaning of the FAP
Tips to avoid breakdowns
- Make long journeys at least once a week.
- Avoid driving constantly at low revolutions.
- Use quality fuel and approved low ash oil.
- Promptly respond to any warning of failed regeneration.
- Perform preventive maintenance every 20,000-30,000 km.
Cleaning methods
Not all DPF cleaning methods deliver the same results. Effectiveness, cost, turnaround time, and risk vary significantly depending on the approach your shop chooses:
| Method | Effectiveness | Removes ash deposits | Requires removal | Estimated time |
| Thermal regeneration (active or forced) | Moderate | No | No | 20–40 min |
| Chemical cleaning with additive | Moderate | Partially | No | 2–4 hrs |
| Ultrasonic cleaning | High | Yes | Yes | 4–8 hrs |
| Professional DPF cleaning machine | Very high | Yes | No | 1–2 hrs |
What’s the best way to clean a DPF?
A professional DPF cleaning machine currently offers the best balance: high effectiveness, short turnaround, and no need to remove the filter from the vehicle. Shops equipped with specialized machines like those from Oxyhtech can complete the service same-day, with results on par with ultrasonic cleaning—but without the risks that come with removal.
Thermal regeneration, while useful in early stages, does not remove the metallic ash deposits that build up over time. For filters with more than 60,000 miles or with advanced blockage, a deeper cleaning method is always necessary.
Do you run a shop and want to offer professional DPF cleaning? Check out Oxyhtech’s DPF cleaning machines and add this service to your offering in just a few days.
DPF by car make: key differences by manufacturer
Every automaker has developed its own diesel particulate filter system. Understanding the specifics of each brand helps drivers take better care of their vehicle—and helps mechanics make faster, more accurate diagnoses.
DPF in Peugeot and Citroën
Peugeot and Citroën were the first manufacturers to fit a particulate filter as standard equipment, back in 2000. Their FAP system uses a liquid additive called Eolys (cerium-based), stored in a separate reservoir and injected into the fuel to help burn off soot at lower temperatures.
- Key feature: when the Eolys reservoir runs dry (roughly every 75,000 miles), the system can no longer regenerate properly and the filter clogs up quickly.
- Specific warning sign: a dedicated FAP additive warning light on the dashboard.
- Common models: Peugeot 207, 307, 308, 407, 3008 / Citroën C3, C4, C5, Berlingo with HDi engines.
- Recommendation: top up the Eolys fluid at scheduled service intervals to prevent premature filter clogging.
DPF in Volkswagen, Audi, SEAT, and Skoda (VAG Group)
The Volkswagen Group adopted the DPF across its TDI engine lineup from 2005 onward. Unlike the PSA system, VAG vehicles do not use a liquid additive—instead, they rely on a high-temperature regeneration process that injects extra fuel during the exhaust stroke.
- Common issue: engine oil dilution caused by the extra fuel injected during regeneration, particularly on vehicles used mainly for short city trips.
- Specific warning sign: oil level rising on the dipstick (oil diluted with diesel fuel).
- Common models: VW Golf, Passat, Tiguan / Audi A3, A4, Q3 / SEAT León, Ibiza TDI / Skoda Octavia, Fabia TDI.
- Recommendation: change the oil more frequently than the standard interval if the vehicle is used primarily for city driving.
DPF in BMW
BMW has fitted DPF systems to its diesel engines as standard since 2007. The system is among the most sophisticated on the market, with multiple sensors continuously monitoring filter load and managing regeneration cycles autonomously.
- Key feature: BMW’s system calculates soot accumulation using mathematical models rather than relying solely on differential pressure, which reduces unnecessary regeneration cycles.
- Common issue: in city driving, regeneration cycles are interrupted when the engine is switched off, causing soot to build up progressively until the filter is fully blocked.
- Common models: BMW 1 Series (116d, 118d), 3 Series (318d, 320d), 5 Series (520d), X3 and X5 diesel.
- Recommendation: avoid turning the engine off immediately after city driving if the regeneration indicator light is active.
DPF in Mercedes-Benz
Mercedes-Benz CDI-engined vehicles have come with DPF as standard since 2008–2009. In newer BlueTEC engines, the DPF works in combination with the SCR (selective catalytic reduction) system and AdBlue fluid for NOx reduction.
- Common issue: DPF clogging in Sprinter and Vito vans used for urban delivery, and regeneration disruption when AdBlue levels run low.
- Common models: A-Class, B-Class, C-Class, E-Class CDI / Sprinter / Vito / GLC and GLE diesel.
- Recommendation: check AdBlue levels regularly; a low level doesn’t just trigger engine restrictions—it can also interfere with the DPF regeneration cycle.
DPF in Renault and Dacia
Renault and Dacia dCi engines have come with a DPF since Euro 5. On the 1.5 dCi engine in particular, the EGR valve and the DPF tend to clog up together, so it’s common practice to service both components at the same time.
- Common models: Renault Mégane, Clio, Kadjar, Captur, Trafic / Dacia Duster, Sandero with dCi engines.
- Recommendation: always inspect the EGR valve when diagnosing a blocked DPF on these makes—treating only one often leads to a repeat failure.
Does your shop service these makes and want to offer professional DPF cleaning? Oxyhtech machines are compatible with all models listed above. View DPF cleaning solutions.
What about filters in gasoline and LPG vehicles?
The DPF is the particulate filter specific to diesel engines—but it’s not the only type of particulate filter found in today’s vehicle fleet.
Gasoline-powered vehicles with direct injection (GDI, TFSI, TSI…) also emit solid particles during combustion. Since Euro 6d, most of these engines come fitted with a GPF (Gasoline Particulate Filter), which works on similar principles to the diesel DPF but has its own specific cleaning and maintenance requirements. Learn more about GPF cleaning for gasoline engines.
Vehicles converted to run on LPG (liquefied petroleum gas) can also feature particulate filtration systems that require specialized servicing. Find out how LPG filter cleaning works.
FAP repair or replacement
When is it necessary?
- When the FAP is physically damaged (internal breakage).
- When it has lost porosity and no longer filters properly.
- When the regenerations have failed repeatedly and the filter is collapsed.
- When the vehicle has been running for a long time in emergency mode.
Important: Replacing an FAP can be costly, depending on the model. Therefore, preventive cleaning is always the smartest and most economical option.
Conclusion: take care of your car’s FAP and avoid costly breakdowns
The car’s FAP is a vital system for reducing pollution and protecting the engine. But like any component, it needs maintenance, cleaning and proper driving to work properly.
The good news is that there are professional and effective methods to keep it clean and operational, thus avoiding costly replacements and complying with current regulations.
Do you have a workshop and want to offer professional FAP cleaning? Do it with Oxyhtech technology: See DPF/FAP cleaning machines
Protect your customers’ engines, reduce emissions and make your workshop more profitable.
Frequently asked questions about the DPF
To encourage DPF regeneration, drive the vehicle at a steady speed of 50–75 mph for at least 20–30 minutes with the engine fully warmed up. This raises exhaust temperatures high enough to burn off accumulated soot. If the regeneration warning light stays on after this drive, take the vehicle to a shop for a forced regeneration using diagnostic equipment.
A properly maintained DPF typically lasts between 75,000 and 125,000 miles. Lifespan depends mainly on driving style: short urban trips significantly shorten it, while highway driving extends it. A professional preventive cleaning every 50,000–60,000 miles can considerably extend the filter’s service life.
Driving with a blocked or damaged DPF causes progressive power loss, increased fuel consumption, and the risk of damage to the turbocharger and EGR valve due to excessive back pressure. In severe cases, the engine may enter limp mode or suffer internal damage. In addition, the vehicle will fail its emissions inspection, and removing the DPF is illegal in most jurisdictions.
FAP and DPF refer to exactly the same component. FAP (Filtre à Particules) is the term coined by Peugeot-Citroën when they introduced the filter on their vehicles in 2000, and it’s widely used in France and Spain. DPF (Diesel Particulate Filter) is the international technical term used throughout the rest of the world, including the UK and the US. Both acronyms refer to the same diesel exhaust particulate filtration device.
Yes. Emissions testing verifies that the vehicle meets the standards it was certified to at the time of manufacture. A removed or severely degraded DPF causes particulate emissions to exceed legal limits, resulting in a failed inspection. Many states and countries also conduct visual inspections to detect tampering with emission control systems.
While a DPF delete is technically possible, it is illegal for any vehicle operated on public roads in the United States and throughout the European Union. A vehicle with a deleted DPF will fail emissions testing, cannot legally enter low-emission zones, and may be subject to significant fines. DPF removal may also void the vehicle’s warranty and, in the event of an accident, may affect insurance coverage.
There’s no fixed limit, but in practice a DPF can be cleaned three to five times over its service life without losing effectiveness—provided the internal ceramic substrate has no physical damage. If back pressure readings remain high after cleaning, or if the filter clogs again in less than 12,000 miles, the ceramic structure is likely compromised and replacement becomes necessary. Learn more about how many times a DPF can be cleaned.
To encourage DPF regeneration, drive the vehicle at a steady speed of 50–75 mph for at least 20–30 minutes with the engine fully warmed up. This raises exhaust temperatures high enough to burn off accumulated soot. If the regeneration warning light stays on after this drive, take the vehicle to a shop for a forced regeneration using diagnostic equipment.
