I must admit i have never heard of any make of car doing a self cleaning thing etc...
Me either, before i saw how this was done in the alfa workshop.
Some months ago, i was present when a 159sw 1.9JTDM came into service, who was running on emergency program due to bad diesel. The yellow control lamp was blinking and the car didn't alow speeds higher than 90 km/h.
The serviceman then connected the car to the computer and ran the DPF cleaning program. This procedure takes about 20 min., where the car is running at cca.3000 rpm - some nasty black smoke from the exhaust. The whole procedure is controled via PC.
While the car was on cleaning mode the mechanic told me, that this is a common isue with the 159 diesel engines - due too slow driving or bad diesel. Slow driving (city area) prevents the engine of making a self cleanig of the DPF.
Trust me, i got this info from my alfa-mechanics.
p.s.: I don't drive slowly.....and had tha same problem with the DPF (PC cleaning was done)
p.p.s.: Not only an issue with Alfa. Ohter brands have same problems with diesels who have the DPF.