For ages Ive been looking for a better understanding of how the DPF works and what things affect it and what style of driving is best for it. In my searching I found this that could be of onterest to some.

Courtesy of ***** ******* Volkswagen Technical Support Specialist Diesel Particulate Filter (DPF)

Detailed below is important information outlining the function and features of the Diesel Particulate filter which all members of your team need to be aware of.

Diesel particulate filters are becoming more commonplace on diesel engines, particularly sizes 2.0L upwards. This is in order to reduce the exhaust emissions as required by European legislation.

The prime reason for a DPF is to reduce particulate matter entering the atmosphere. Particulate matter is found in the form of soot, which is produced during diesel combustion. The DPF traps most of the soot which would normally travel down the exhaust and into the atmosphere. The DPF can hold a certain amount of soot, but not a huge quantity and therefore it needs to go through a process called ‘regeneration’ in order to clear the soot loading. When the soot goes through a ‘regeneration’ process it will be converted to a much smaller amount of ash. The ash is non-removable. There are two types of ‘regeneration’, passive and active.

During long motorway journeys, passive regeneration will occur. This needs no intervention from the engine control unit. Due to the raised exhaust temperatures on a long journey (temperatures between 350 and 500°C), the procedure occurs slowly and continuously across the catalytic-coated (with platinum) DPF. The catalytic-coated DPF is situated close to the Engine, therefore the exhaust gas temperature is high enough (500°C) to ignite the soot particles. Due to this soot is burned-off and is converted into a smaller amount of ash.

Active ‘regeneration’ is when the ECU intervenes when the soot loading in the DPF is calculated to be 45%. The procedure lasts for about 5 – 10 minutes. Specific measures are taken by the ECU to raise the engine exhaust temperature to above 600°C, these include switching off the exhaust gas recirculation and increasing the fuel injection period to include a small injection after the main injection. The soot particles are oxidised at this temperature.

The ECU will trigger a regeneration process, if for some reason this is aborted, ie. customer slows down, stops etc, the process will be resumed when regeneration conditions are once again met, above 60km/h (38mph). This will continue for 15 minutes.

If after 2 attempts of 15 minutes, a successful regeneration has not been possible, the loading will increase. At 50% soot loading, the ECU will continue to maintain maximum exhaust temperatures of 600°C to 650°C to cause a regeneration process. The system will try to run a regeneration process for 15 minutes. If unsuccessful, the system will repeat this process for a further 15 minutes, if still unsuccessful, the DPF light on the driver display panel will then be lit.

The owners handbook states, the DPF symbol lights up to indicate that the diesel particulate filter has become obstructed with soot due to frequent short trips. When the warning lamp comes on, the driver should drive at a constant speed of at least 60 km/h for about 10 minutes. As a result of the increase in temperature the soot in the filter will be burned off. If the DPF symbol does not go out, the driver should contact an authorised Volkswagen repairer and have the fault rectified.

At 55% soot loading the DPF light is lit on driver display panel. At this point the customer should follow the advice in the handbook. If they ignore this information and continue driving the vehicle until the soot loading reaches 75% without successful regeneration, additional warning lamps will light up. At this point the customer will also be complaining of lack of power, etc.

At 75%, regeneration is still possible with the use of the VAS tester. Only when the loading is above 95%, is it necessary to replace the DPF unit.

it necessary to replace the DPF unit.

Operating Status System Response

45% DPF Load Level 1 Normal Regeneration

50% DPF Load Level 2
Regeneration at maximum exhaust temperatures

55% DPF Load DPF lamp Regeneration from 60 km/h onwards ("See operating manual")

75% DPF Load DPF, SYS and MI lamp Torque limitation, EGR deactivation,

Regeneration via VAG tester only 95% DPF Load Replace the DPF Unit

The Warranty department has confirmed that if there is no fault on the vehicle and DPF regeneration has been unsuccessful due to the customers driving style and the customers failure to comply with the instructions in the handbook, DPF replacement will not be paid for by warranty.

Common causes for complaint

• Frequent short journeys – Regeneration conditions are not met.
Not recommended for sale in the Channel Islands and inner city driving.

• Customers who continue to drive the vehicle with DPF light on – Continued driving with the DPF light on and without successful regeneration results in excessive soot loading of the DPF, to a point where it is above 95% loaded. At this point regeneration is not an option and replacement of the DPF is necessary.

• Fault 18434 particle filter bank 1 malfunction – Common fault code. This does not only relate to the DPF itself, but the entire exhaust gas handling system. This can be caused by defective temperature sensors, pressure sensors, additive system components (if applicable), poor connections, wiring issues, etc.

Important Information

• Before diagnosing a problem vehicle or attempting to perform an emergency regeneration, it is important to obtain a full diagnostic log and read out relevant measured value blocks. These MVB’s contain important information on the condition of the DPF system and are essential in diagnosing the fault. When the DPF light is illuminated, it does not necessarily mean that the DPF requires regeneration. For further advice, please contact Technical Support with the information from the diagnostic log and MVB data.

• If a problem vehicle arrives with the DPF light, the engine management light and the emissions light on. If during your diagnosis and reading of relevant MVB’s, you find that the soot loading exceeds 75% (but is still below 95%), an emergency regeneration procedure must be performed with the VAS tester. Further to this, the customer needs to be educated. They need to understand why the lights have appeared on the dash panel. Their attention needs to be brought to the owners handbook instructions, so that they are aware of what the DPF light means and what to do when it appears. This should prevent unnecessary repeat visits for regeneration purposes.

I have also found that as the car gets older 30K+ miles, you will notice that the regeneration takes place more often.

ALWAYS, check your oil before any long journey, as DPF regeneration can use a fair bit of oil.

Interesting how low a speed active regen needs.

Edited by Stanb Sevento on 05/05/2017 at 16:18