A diesel particulate filter (or DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.
This is accomplished by programming the engine to run at a higher temperature than normal(when the DPF is full) to oxidize the ash and soot in the DPF .This is called filter regeneration. This happens normally in most diesel engines and you will not be aware that it is taking place. However if you do a lot of city driving where the engine struggles to get to its operating temperature then you should drive the car on the open road for a period of 30 minutes at a speed above 65km. This will allow the DPF to burn off the excess soot and ash.
Lack of regular servicing will lead to contamination of the filters, fuel injectors and turbochargers which will lead to the failure of the DPF which is very expensive to replace.
The DPF and catalytic convertor are designed to keep the cars emissions within the regulations specified for your car. This is what the NCT checks and emissions are a common and costly failure.
If the warning light appears (as pictured above) you should go to your Team Autocentre member to have the DPF dealt with immediately as to ignore it will prove very costly.
STP DPF cleaner is designed to maintain your DPF.
STP Fuel Injection System Cleaners.