To prevent blockage of the DPF the engine ECU triggers a regeneration process after every 1000 km (620 miles) at the latest. During this process the exhaust temperature is raised to about 600 °C (1112 °F) and the soot in the filter is burnt to ash.

A lot of short trips or urban driving lead to a low efficiency of the particulate filter regeneration and in the long run this may result in blockage of the filter and error memory entries in the engine ECU. The regeneration can not be started in this case, because the function is blocked.

For a regeneration the following conditions have to be met:

• coolant temperature higher than 75 °C (167 °F)
• exhaust temperature higher than 240 °C (464 °F)
• the fuel reserve warning lamp is off
• no error memory entries from the air mass system, exhaust system or sensors in the engine ECU
• constant driving speed larger than 60 km/h (37 mph), optimal speed is about 100 km/h (62 mph)

For an optimal regeneration the car has to be driven at least 20 minutes with a constant speed of 100 km/h (62 mph) after the regeneration has started.