Customer information – Diesel Particulate Filters (DPF)

Our level of telephone enquiries are currently on the increase regarding problems with Diesel Particulate Filter, (DPF’s).

Some customers are requesting Technical information, others just want to know what to do and how to fix it, albeit, not always that simple.

We thought it paramount to present an understanding of why DPF’s are fitted, a brief explanation of Euro 6 and how to manage your diesel engine emissions effectively and efficiently.

The diesel particulate filter (DPF) is designed to trap and store the soot produced by a diesel engine during normal driving. Exhaust gases containing soot enter the DPF and soot is trapped inside the filter, resulting in cleaner exhaust gases and reduced emissions. From 2005, vehicle manufacturers were required to reduce diesel emissions through the increasingly stringent Euro Emission standards. As a result, the Euro 5 standards that came into force in 2009 saw particulate matter levels reduced from 25 mg per Kilometre, as specified by Euro 4, in 2005, to just five mg per kilometre. In order to achieve this greatly reduced level, DPF filters are now fitted to virtually all diesel vehicles.

Euro 6 regulations is the next progression from 01 Jan 2015.  Euro 6 specification is aimed at targeting a reduction in nitrous oxides, or ‘NOx’, because they are a significant greenhouse gas and air pollutant.

Indeed, the greenhouse gas effect of nitrous oxide itself is hundreds of times greater than carbon dioxide: it is the fourth largest contributor to greenhouse gas global warming.

The cut is large: an Euro 6 diesel car must emit more than 50 per cent less nitrous oxides than a Euro 5 diesel. The cap is 80 mg/km, compared to a 180 mg/km allowance for Euro 5 diesels. The reduction from Euro 4 to Euro 5 was 20 per cent, showing how severe the reduction demanded by Euro 6 is.

Back in 2000, the nitrous oxide limit was 500 mg/km, illustrating how large the reduction has been.

Local air pollution is also being tackled by Euro 6 standards with a cap on emissions of hydrocarbons and nitrous oxides from diesel cars. These are limited to 170 mg/km, compared to 230mg/km with the current Euro 5 regulations.

This is why Euro 6 regulations are so significant. Diesel engines naturally produce higher levels of nitrous oxides than petrol cars. Euro 5 was a daunting target for diesel engines to meet, but Euro 6 is perhaps even more challenging.

DPFs need to regenerate to function correctly – if left they become blocked and stop operating. This will cause the vehicle to suffer a lack of power due to a high level of back pressure in the exhaust. The engine management and emission warning lights will come on to warn the driver of a problem.

Depending on driving style, regeneration takes places every 300 to 500 miles, when the DPF is filled to around 45-50% of its capacity.

Time for a regen

There are three different regeneration modes to clear the soot in the DPF:

Passive Regeneration takes place while driving when engine load elevates exhaust temperatures enough to burn small amounts of soot. These temperatures can range from 200ºC to almost 600ºC and requires no action from the driver or engine control system.

Active Regeneration can occur while driving or when the vehicle is not moving and the engine is idling, to burn large amounts of soot. The process is initiated by the engine management control module software and only when certain conditions are met. Typical exhaust temperatures will range from around 400degC to over 600degC and requires no action from the driver.

Manual Regeneration is essentially the same as active regeneration but is initiated by using a diagnostic tool. There are two modes of manual regeneration – static and dynamic. Static is when the vehicle is stationary but due to the very high temperatures around the DPF, this could risk damaging wiring and other components. Many manufacturers are now disabling static regeneration, as driving the vehicle allows airflow under the vehicle to cool wiring and components close to the DPF.

Manual regeneration is often required when vehicles are driven at insufficient speed to allow passive or active regeneration to be carried out automatically by the engine management system. At this point, as long as the DPF is not severely blocked with over 90% capacity filled, a diagnostic tool can be used to perform either a static (up to 60% capacity filled) or dynamic regeneration to clear it. It’s also important to remember that all exhaust and engine management system components need to be in full working order for DPF regeneration to take place successfully. If not, the engine management control module software will disable manual regeneration and provide a ‘failed’ or ‘unsuccessful regeneration’ message on the scan tool display.

Reasons for failed or unsuccessful regeneration include:

  1. DPF over 90% filled. This requires replacement of the DPF and will require a diagnostic tool to reset DPF values in engine management control software after the new DPF has been fitted.
  2. Diesel fuel level in tank is under a quarter (a minimum of 20 litres of fuel is required).  We recommend using Shell V Power Nitro + or BP Ultimate.  The reason is that these fuels have increased cleanliness property’s and anti rust components within the fuel protecting diesel fuel injection systems.  A cleaner fuel that cleans and protects your engine. Yes, a little more expensive, but well worth the cost.
  3. On vehicles that use oil quality monitors, if the quality of oil is degraded or diluted due to excessive use of mode 2 regeneration, the oil will have to be replaced before regeneration can be carried out. Using pre oil drain treatments, if used correctly, ensures you remove the majority of sludge that can contaminate oil supplies to important components within your engine.  This process allows the new refreshed oil to present a better performance due to the lack of contamination from the unclean oil left in your engine.   
  4. Any fault codes in the engine management system will prevent a regen; including glow plug circuit, DPFE sensor, exhaust temperature sensors or Lambda sensors, which are all used to control and monitor the manual DPF regeneration process. The faults will have to be repaired and the fault codes cleared before regeneration can be carried out.
  5. Fixed life reached. The DPF is a renewable item and once the given mileage is reached it will not regenerate (this can be as low as 75,000 miles). Typically, we have replaced a number of 5 series BMW DPF’s at 120,000 miles.  A diagnostic tool will be required to reset the DPF fixed life values in the engine management control software after a new DPF has been fitted.

In Conclusion

If your vehicle has the glow plug light illuminated or flashes intermittently depending what model you drive the car will most likely be in it’s REGEN mode.  It’s important  NOT switch the engine off while your car is in this mode, carry on driving until the light extinguishes, this could take upto 20 – 30 minutes.  Failure to do so could illuminate the EML (Engine Management Light) even placing the car into LIMP MODE.  This could restrict the full power of the car and will require a visit to the workshop for a diagnostic check & report.  By completing the REGEN process this will most likely be prevented.  If the EML (Engine Management Light) illuminates (sporadically or stays on) the next step is to book an appointment at the workshop to carry out a diagnosis on the related problem. Failure to carry out this advice will most likely lead to an expensive repair which could have been avoided.  If in doubt, please just give us a call, we want to help, the advice is free!


The engineering process on DPF’s is relatively simple when you break it down into digestible chunks.  For the driver it’s even easier.  His/her responsibility is using a quality, correct grade performance oil and the correct cleaning performance fuel.  My Team have conducted hours of research, repair time, blood sweat and a few tears into our methods of dealing with these type of repairs.  We have the technology and experience to support the majority of DPF repairs.  Removal of the DPF and remapping is not a way to remedy these problems and causes other major issues with the car’s engineering.

It’s good maintenance to ensure your car has a yearly oil & filter changes (with treatments) if you are doing low mileage annually.  This will help avoid any DPF problems.  In addition, we advise using Shell or BP fuels. This will reduce your carbon emissions and maintain your cars performance and efficiency, saving you money long term.

Please read your owners manual for further instructions.  We cannot place every German Manufacturers DPF regen details on this page.





Written by