Diesel Particulate Filters are exactly that..... A filter to trap diesel particulate matter (Soot/Carbon) from the exhaust gasses to prevent them entering the atmosphere.
How do they work? By filtering out carbon and trapping it inside the DPF. Once full, the engine control module will initiate the cleaning cycle, called 'regeneration', whereby the DPF is heated to around 550-650°C. At this temperature, carbon burns from a solid into a gas (Carbon Dioxide), and the remaining solid matter is a mineral (Ash)... Ash cannot be burned, nor can it be dissolved, but it is fine enough to mostly pass through the filter, so you're left with a clean filter again, and no harmful particles have exited the exhaust into the atmosphere.
The ONLY way a DPF fails is if it cracks or crumbles internally, which can occasionally happen and will allow carbon to pass through it unfiltered or cause a blockage by itself, but it isn't as common as most think.
In the majority of cases, a DPF which has become blocked, is not blocked because it has failed, or needs replacing. It's blocked because something else has faulted and caused it to either fill up with excessive soot from the exhaust, or because the regeneration process is repeatedly interrupted, causing it to continue to fill rather than regenerate. Replacing a DPF without correctly diagnosing the root cause of the failure will only lead to the exact same issue being repeated in a few weeks or months time, and removing it is illegal.
Diagnostics by someone competent is the only way to remedy this. Anything from an intake air leak, to a faulty intake air temperature sensor, faulty injectors, faulty exhaust gas temperature sensors (EGT), or many other contributory causes can lead to a problem with the DPF, but mechanics who understand exactly how they work, and what causes them to block or fail to regenerate, are massively in short supply.
Do DPF cleaners work? Mostly yes, but they will only help to clean the filter. They won't cure a fault elsewhere thats causing it to block in the first place. Once a fault which causes the DPF to block has been identified and remedied, a DPF cleaner can help to regenerate it and get it clean again, but they're often mis-used and seen as the 'cure' to the problem. If the real fault is not correctly diagnosed and repaired, the DPF will only become blocked again.
In short, a DPF will collect and burn carbon repeatedly over the life of the vehicle, and generally do not fail. Mis-diagnosis is the number one cause of a DPF either being uneccesarily replaced or deleted. They do have a service life, which generally is around 250,000 miles, but some will go on to perform perfectly fine well beyond this mileage provided everything else with the engine is as it should be and operates correctly.
