All particulate filter systems include some means of regeneration. The three most common types of regeneration are active, passive and forced regeneration.
The active system works off a filter load limit or sensors reading exhaust backpressure or the ‘soot load’ of the filter, activating timing adjustments to the fuel injection which in turn increases the exhaust temperature, initiating the burning of the soot and regenerating or clearing the filter. Depending on the vehicle brand, this type of DPF regeneration can also be initiated by the vehicle ECU every 400 - 600 kms or depending on vehicle use. It also takes around 10 minutes to complete.
Some manufacturers use passive regeneration. For these vehicles passive regeneration generally takes place on the motorway where exhaust temperatures are higher. This type of system can have an integrated oxidizing catalytic converter located close to the engine where exhaust gases are hot enough so that passive regeneration is possible. Passive regeneration relies on the exhaust temperature being high enough to automatically burn off, and/or using the ECU to alter the vehicle timing to control the process. In city driving or short trips the regeneration my not take place fully, leading to blocking of the filter. This can lead to higher fuel consumption and a visit to the mechanic for cleaning or replacement.
When the vehicle displays second stage DPF warning lights it will go in to ‘limp mode’ and should be taken to a garage or dealer to ascertain the extent of the problem. A forced regeneration involves the garage using a computer program to run the car, initiating a regeneration of the DPF. This will also require changing the engine oil & oil filter.
Over time "ash," produced by the incomplete burning of the various engine lubricants, builds up inside the filter leading to plugged cells and increased exhaust backpressure. Even though the normal exhaust "soot" is oxidized and burned up during filter regeneration, the "ash" is unable to be removed by this process and must be manually removed at a diesel particulate filter service center with a specialized DPF servicing machine. The "ash" removed during the DPF cleaning is considered hazardous material and needs to be handled according to local laws and regulations. Failure to service a DPF when necessary may lead to damage to the filter, engine performance problems, and more expensive ash removal processes.