In recent years modern diesel engines have become increasingly more powerful, fuel efficient and responsive, all while being significantly cleaner and environmentally friendly. There have been numerous design and technological advancements in diesel engines. BMW and MINI engines are at the forefront of technology with features such as variable geometry turbochargers and high precision direct injection providing the ultimate in diesel performance.


What does a diesel particulate filter do?

A diesel particulate filter (DPF) catches soot particles from the exhaust after exiting the turbocharger. This reduces carbon emissions (CO2) that enter the atmosphere. If you look back to the early diesel engines, when the driver accelerated, there would be a characteristic cloud of black smoke exiting the tail pipe. This was a normal characteristic but required significant refinement to meet modern emission requirements. Hence the diesel particulate filter was born.

As the filter progressively collects the soot the pressure differential inside the filter increases. Once the pressure differential or time elapsed exceeds a preset value the DDE signals for a regeneration. Extra fuel is then injected, post combustion to heat the particulate filter and the exhaust gas recirculation system is disabled, causing the soot to burn off and be converted to ash. This process cleans the particulate filter and maintains engine performance.


What causes my diesel particulate filter to become clogged?

There are numerous causes of a clogged DPF. Driving conditions, the use of low quality fuel, incorrect engine oil or a faulty sensor are all possible causes of DPF failure. Our trained BMW technicians are experts in their field, and are able to quickly and effectively diagnose your clogged particulate filter, recommending the most efficient repair procedures to restore your vehicles DPF to it’s optimal condition.


What driving conditions can cause my diesel particulate filter to become clogged?

The most common cause of diesel particulate filters becoming clogged is excessive short trips. Regular city driving produces large amounts of soot. The particulate filter is very effective at collecting the soot and storing it for regeneration at a later stage. If the vehicle is rarely driven at freeway speeds then there may not be enough time for the particulate filter regeneration procedure to be completed. We recommend to drive the vehicle at freeway speeds at least 30 minutes once a month. The vehicle requires a steady cruising speed to be maintained to perform and effective regeneration. Driving in traffic will often not produce the desired regeneration effect and can effect vehicle performance.

Regular servicing of your BMW or MINI is also critical to ensure correct operation of the diesel particulate filter. Modern diesel engines require the use of an engine oil with low SAPS. SAPS stands for “Sulphated Ash, Phosphorous and Sulphur” A low SAPS engine oil is specially formulated with reduced levels of these elements than a standard engine oil. Stokes and Renk always use BMW approved Castrol Fully Synthetic Engine Oil to ensure our customers vehicles continue to provide the highest standard of performance and maintain their legendary BMW reliability.


How do I know if my diesel particulate filter requires service or repair?

During your vehicle service, the technicians at Stokes and Renk check the exhaust back pressure at various engine speeds. This is a controlled procedure that we initiate with our Autologic scan tool. We then monitor the pressures to ensure they are within their target levels. If any faults are present, our expert technicians will advise the vehicle owner and recommend a course of repair. 

In extreme cases the driver is notified on the vehicle iDrive screen or instrument cluster and engine performance is significantly reduced, to protect the engine and turbocharger. It is recommended to have the vehicle repaired as soon as possible as continual driving may cause significant damage to the vehicle particulate filter system. This can often be very costly to rectify.


What repair options are available for my diesel particulate filter?

Stokes and Renk can advise on the most cost effective course of repair on your BMW or MINI particulate filter. Often if the particulate filter is only marginally clogged, our technicians can perform a forced regeneration process. This is often useful if the vehicle is only driven for short trips, mainly in the city. This is completed using our Autologic scan tool, where a technician will force regeneration and drive the vehicle at freeway speed. This is only possible if there are no faults in the engine management (DDE) that relate to the particulate filter system.

If there are faults present in the DDE for the particulate filter system, our technicians will first advise a course of action to rectify the faults and then perform a forced regeneration. 

If the particulate filter is heavily laden with soot, forced regeneration may become impossible. If this situation is present, our specialist BMW mechanic will remove the particulate filter from the vehicle. Depending on the damage to the filter it may be possible to recondition the filter, at a fraction of the cost of a new BMW filter. This procedure normally takes between 3-4 days to complete. If you require a replacement vehicle during this period, contact the team at Stokes and Renk!

The final option is to replace the particulate filter with a new unit. We only recommend this option in extreme circumstances, where significant damage to the particulate filter has occurred.