ACTIVE DPF REGENERATION SYSTEM
When the soot loading in the filter reaches a set limit (about 45%) the ECU will initiate post combustion fuel injection to increase the exhaust temperature and trigger regeneration. If the journey is a bit stop/start or you take your foot off the accelerator while the regeneration is in progress, it may not complete and the warning light will come on to show that the filter is partially blocked.
PASSIVE DPF REGENERATION SYSTEM
Passive regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. Because many cars don’t get this sort of use car manufacturers have to design-in ‘active’ regeneration where the engine management computer (ECU) takes control of the process.
A car which is primarily used for motorway use will generally run at warmer temperatures and therefore produce far less particulate matter than one used in a stop/start city environment. A vehicle used on the motorway is also going to be able to regenerate more often and effectively as it is in the perfect driving environment for the regeneration process to occur.
The operation of the DPF is controlled by the ECU and requires multiple signal feeds from various sensors in order to operate effectively. The most common type of DPF runs two pressure sensors and a varying number of temperature sensors. There is differential pressure sensor mounted in the engine bay which picks up the pressure both before and after the DPF. It is the variance in pressure between these two pick-ups which allows the ECU to calculate the percentage saturation of the DPF. Once the ECU establishes the saturation level it is able to force a regeneration cycle. The progress of the cycle is monitored by the temperature sensors and takes constant feedback from the differential pressure sensor which enables to know when the burn off process is complete.
DIESEL PARTICULATE FILTER ADDITIVES
Some manufacturers use additives to reduce the ignition point of the soot particles by secreting small amounts of fluid into the fuel tank which mixes with the fuel. The additive is a service item and is designed to require refilling every 75,000 miles approximately. Ignoring the warning for low additive will mean the DPF will not regenerate properly and will almost certainly require a new DPF. Certain models of vehicles however require the DPF to be changed with the additive top up which makes for expensive servicing bills.
DO THEY REQUIRE MAINTENANCE?
A DPF has a design life of around 75,000 miles but this can be subject to large variation depending on vehicle use and engine condition. Every time the ECU forces a regeneration cycle it burns the particulate matter down to a much smaller amount of finer soot, they don’t get completely removed from the filter. Over time, the fine soot content builds up to a point where a regeneration cycle is no longer able to be performed; at this point the filter either needs emptying or replacing.
COMMON CAUSES FOR DPF FAILURE
There are a multitude of reasons a DPF can fail, the most common are highlighted below:
Notes regarding DPF Removal