DPF Regeneration is the term given to the DPF cleaning process where the exhaust temperature is raised in an attempt to safely burn off any particulate matter captured in the DPF Filter. When the DPF filter reaches a soot saturation level (fill level) of between 25-45% the on-board engine ECU will activate a Regeneration Cycle.
Please note: The DPF Regeneration cycle should not be interrupted and can take up to 1 hour to complete.
In order for the engine ECU to activate a regeneration cycle, it needs to be able to calculate how much particulate soot is trapped in the DPF filter. The most common technique used is by fitting a Differential Pressure Sensor with two pressure pipes. One pipe will be mounted at the face of the DPF filter and one to the rear of the DPF filter. The difference of pressure will then be calculated by the ECU to determine how blocked the filter is.
Some manufacturers have been known to use pressure sensors with just a single pressure pipe i.e. Vauxhall Corsa 1.7CDTi and some even have two pressure sensors with three pressure pipes i.e. Mitsubishi Shogun 3.2D.
The average exhaust gas temperature when driving can be around 150-300 degrees celcius. In order to carry out a successful regeneration, the exhaust gas temperatures must reach levels of at least 600 degrees celcius minimum and have been known to reach up to 850-900 degrees celcius. In order to achieve the higher exhaust gas temperatures, manufacturers have used various methods such as:
- Additive Fluid Systems
- 5-Cylinder Engines
- 5th Injector in Exhaust
- Pre-Cycle & Post-Cycle Injection
There are also temperature sensors in the exhaust (normally two or three) and these will be placed as follows:
- At the Turbocharger (Before Catalytic Converter)
- After the Catalytic Converter (Before DPF)
- After the DPF Filter
This will measure the temperatures at all three sections of the exhaust and the information sent back to the ECU will help to determine how much diesel/additive will be required to reach the optimum exhaust gas temperatures to complete a successful DPF Regeneration Cycle.
Important: If any of the above sensors are not working correctly, it may cause the DPF Regeneration Cycle to fail. This will result in excessive soot build up and further problems may arise.
Once a DPF Regeneration Cycle has been activated, you may see a warning symbol appear on the dashboard/speedo to indicate the vehicle is now in Regeneration Mode. When in regeneration mode you must not switch off the engine, otherwise the regeneration cycle will end and fail. This will cause the DPF to block up even more and potentially cause damage to the vehicle – so it’s important that when this light appears, you must enter a motorway/dual-carriageway and carry out a regeneration as described in your owners manual.
Example Regeneration Instructions: If the DPF light appears on the dashboard, you must drive the vehicle at 40 mph for a minimum of 15 minutes until the DPF light goes out. This will indicate a successful regeneration of the DPF filter. If the DPF symbol does not go out, the driver should contact an authorised dealership and have the fault rectified.
If a DPF Regeneration cycle fails, the ECU may attempt a second regeneration depending on how much the DPF filter has blocked up. There is a safety cap which does vary depending on the vehicle but generally the ECU won’t allow you to regenerate anything over 80% blocked as this could run the risk of further damage and even in extreme cases a fire. In such instances you would normally be advised to Clean the DPF Filter or have the DPF Removed.
Note: Most dealerships will not tell you the option of having the DPF removed and may even advise against this option.
Dealerships and most local workshops will not have the specialist programming equipment required to re-program and adjust certain parameters in the ECU and therefore will not be able to offer the specialist “DPF Removal” service to you.
If you do a lot of local town driving then the DPF system may try to regenerate more often because town driving is a lot of stop-start and in this driving style the exhaust gasses can never reach high enough temperatures to burn off any soot. Soot will be collected a lot quicker and the build up in the DPF will happen more often. This will of course reflect negatively on the economy of the vehicle.
If the DPF light comes on and you successfully complete a DPF Regeneration cycle, you will notice that the DPF light will automatically gone off. You might also see a puff of smoke exit from the exhaust which is perfectly normal. You may then continue on your journey until you next see the DPF light come back on. There are several factors that can affect how often your DPF Regenerates and in the long run, the life expectancy of your DPF Filter:
- Grade of Engine Oil
- Grade of Diesel
- Driving Style
- Use of Additives
- Wear of Other Components
For example: The use of supermarket fuels along with infrequent oil changes and a city “stop-start” driving style may initiate more frequent DPF Regenerations and cause the filter to block up a lot quicker.