Faced with a clogged DPF the options look many, but they boil down to four. None is right in absolute terms: it depends on what is inside the filter, soot or ash, and on the condition of the monolith. Let us look at them one by one.
Forced regeneration
Started with the diagnostic tool, it brings the filter to high temperature and burns off the soot. It is quick, needs no removal and works well on a soot-loaded filter.
Its limit is that it leaves the ash inside: on a high-mileage filter the benefit is short-lived. And with too much soot it is risky, because combustion can overheat and crack the monolith.
Additives and “DPF cleaner” products
There are two kinds: fuel additives, which lower the soot combustion temperature, and products sprayed into the filter through a sensor port and followed by a regeneration. They can help as prevention or with light soot clogging, but neither removes ash. On an ash-saturated filter they are money badly spent.
Cleaning the filter
The filter is removed and cleaned off the vehicle. It is the only job that removes both soot and ash. There are two main methods:
- Hydrodynamic washing. The filter is connected to the machine with dedicated adapters, without cutting the canister; a liquid with detergent flows through it in a closed loop, usually against the exhaust flow, carrying away particulate and ash. Drying and back-pressure measurement follow. It works at low temperature, with no thermal stress.
- Thermal and air cleaning. The filter is baked in an oven to burn the soot, then the ash is blown out with compressed-air pulses. It is common on heavy vehicles, but cycles are long and the monolith goes through one more thermal cycle.
Either way, cleaning only makes sense if the monolith is intact: it must be checked first, and the back-pressure measured afterwards is what certifies the result. If you would like to bring this work in-house, we wrote a guide on how to open a DPF regeneration centre.
Replacement
It is the only choice when the monolith is cracked, melted or its catalytic coating is compromised, or when the filter efficiency code is confirmed after checks. On an intact filter, however, it is the most expensive option: a new filter, especially an OE one, often costs several times a cleaning.
DPF removal: why not
Emptying, removing or disabling the particulate filter by software tampers with a type-approved emission control system. It is prohibited by the Italian Highway Code, makes the vehicle non-compliant with its registration, and at the roadworthiness test smoke opacity and diagnostic checks can reveal it. The workshop carrying out the job also bears direct liability. And the particulate the filter traps is precisely the most harmful to health.
The comparison in one table
| Option | Soot | Ash | Damaged monolith |
|---|---|---|---|
| Forced regeneration | Yes | No | No (can make it worse) |
| Additives | Partly | No | No |
| Filter cleaning | Yes | Yes | No |
| Replacement | Yes | Yes | Yes |
| Removal | Not an option: illegal |
How to decide
- Remove the upstream cause: no work on the filter lasts if the engine sends too much particulate or oil into the exhaust.
- If back-pressure returns to normal after a complete forced regeneration, the problem was soot: you are done.
- If it stays high, the filter is full of ash: remove it and check the monolith.
- Intact monolith: cleaning. Cracked or melted monolith: replacement.
Frequently asked questions
Does a washed DPF last like a new one?
If the monolith is intact and the upstream cause has been fixed, a cleaned filter works again with a back-pressure close to the original. How long it then lasts depends, as with a new filter, on engine, oil and vehicle use.
Does washing damage the catalyst built into the filter?
Hydrodynamic washing works at low temperature and with specific products precisely so as not to harm the monolith and the catalytic coating. The real risk for the catalyst is excessive regeneration temperatures on an overloaded filter, not the washing.