Discover all the problems with your diesel particulate filter (DPF) in 2025: causes, clear symptoms, and professional solutions. A comprehensive guide with expert advice to avoid unnecessary costs.
WHAT IS A PARTICULATE FILTER (FAP)?
The particulate filter, known as FAP , is one of the most discussed—and often misunderstood—components of modern diesel cars. It serves to drastically reduce the fine particles emitted from the exhaust.
How does it work? Simple (but not too simple): it traps particulate matter and periodically burns it during regeneration , transforming it into less harmful ash.
Many drivers see it as an “enemy” because it can cause problems, but in reality it is an ally of the environment and also of the engine, if used and maintained properly.
Recommended Article: Best DPF Cleaner Additive: A 2025 Guide to Cleaner Diesels
DIFFERENCES BETWEEN FAP AND DPF
I'm often asked: "But are FAP and DPF the same thing?"
-
FAP is the term used by Peugeot, Citroën, and Renault. It uses an additive (cerin) that lowers the combustion temperature of particulate matter.
-
DPF (Diesel Particulate Filter) is the more generic term used by other manufacturers, usually without additives.
Essentially, they do the same job but with slightly different approaches.
✅ Want to learn more about these engines? Check out PSA 1.5 BlueHDi engine recalls: problems and official checks
WHY IT IS MANDATORY ON MODERN DIESEL CARS
From 2009 onwards (Euro 5 and Euro 6 standards), there is no escape: the FAP is mandatory.
-
Reduces harmful emissions.
-
Helps meet environmental standards.
-
It is essential for vehicle approval.
For those who travel a lot of miles, especially in the city, knowing more is essential to avoid costly problems .
MOST COMMON FAP PROBLEMS
I speak here as a spare parts dealer who hears customers say every day: "My FAP light is on, what do I do?"
The most typical problems:
-
Blockage due to short journeys → regeneration is not completed.
-
Regenerations interrupted → the filter fills up too much.
-
Faulty sensors → incorrect readings blocking regeneration.
-
Control unit errors → “emergency” mode with limited power.
Many drivers don't know that driving style matters a lot .
SYMPTOMS OF A CLOGGED OR MALFUNCTIONING DPF
The FAP warns you when it can't cope anymore. How do you recognize it?
-
Check engine light or message on dashboard.
-
Loss of power → car in recovery.
-
Significant increase in consumption.
-
Black smoke or strange smell from the exhaust.
-
Acceleration is rough or erratic.
✅ Expert advice: Don't ignore the warning light . It's best to take it to the garage immediately to avoid more serious damage.
MAIN CAUSES OF FAP PROBLEMS
The FAP doesn't clog up "by bad luck." There are always specific causes behind it:
-
Intense urban use → short trips = incomplete regeneration.
-
Neglected maintenance → dirty air or fuel filters.
-
Poor or unused additives → rapid accumulation of soot.
-
EGR system or injector problems → more particulate matter produced.
-
Low quality fuel → less clean combustion.
✅ Want to really save money? Take care of your maintenance.
Find out how: Low-cost maintenance for the Dacia Sandero: how to save in 2025
HOW TO PREVENT FAP PROBLEMS
Many people think that FAP is an "inevitable problem." That's not true! Prevention is possible (and recommended).
PRACTICAL ADVICE
-
Take long, steady journeys every now and then → motorway or suburban roads lasting 20–30 minutes to help regeneration.
-
Use quality, manufacturer-approved additives that help keep the system clean.
-
Respect the coupons , preferably in a specialized workshop → they check sensors, EGR, injectors.
-
Watch out for warning lights → don't ignore them.
HOW TO FIX A CLOGGED DPF
If the filter is already clogged, don't panic: there are solutions.
FORCED REGENERATION
-
It's done in the workshop.
-
The control unit is “forced” to regenerate.
-
It costs little, ideal for light blockages.
CHEMICAL OR ULTRASONIC CLEANING
-
Requires filter disassembly.
-
Washing with specific products or ultrasound.
-
Removes accumulated soot well.
FILTER REPLACEMENT
-
Only necessary in the most severe cases.
-
High cost.
-
Recommended only when there is no other alternative.
✅ Tip: Always get a professional diagnosis before spending money unnecessarily.
INDICATIVE COSTS (QUALITATIVE APPROACH)
-
Forced regeneration: the cheapest → routine maintenance.
-
Professional cleaning: medium cost → perfect solution if the filter is not damaged.
-
Replacement: high cost → only if essential.
The trick to saving? Prevention and regular maintenance .
WHEN TO CONTACT A PROFESSIONAL
Avoid improvised DIY. This is why going to a specialized workshop is always the right choice:
-
Accurate diagnosis with professional tools.
-
Safe forced regeneration.
-
Check for any EGR or injector related problems.
-
Software updates.
-
Warranty on labor and spare parts.
✅ More maintenance tips: Dacia Sandero maintenance: costs and advice 2025
Frequently Asked Questions About Particle Filters
DOES THE FAP NEED TO BE CLEANED OR REPLACED?
Depends:
-
If it is not damaged, professional cleaning is more than sufficient.
-
Replacement is only necessary in cases where the filter structure is compromised.
WHICH ADDITIVES TO USE?
Only quality products, preferably manufacturer-approved . They improve combustion and facilitate regeneration.
CAN I DO THE REGENERATION MYSELF?
-
Theoretically yes, but it is strongly discouraged .
-
A poorly performed forced regeneration can damage the engine or solve nothing.
-
It's always better to rely on a professional.
CONCLUSION
The particulate filter isn't an enemy, but an ally of the environment and your diesel engine. As a parts dealer, I recommend:
-
Understanding how it works.
-
Recognize the symptoms of problems.
-
Perform regular maintenance.
-
Use quality additives.
-
Always consult a qualified professional.
This way you will avoid unnecessary expenses and keep your car in perfect shape for years.
