Diesel Particulate Filter (DPF)
Compiled by Chris Hugo, Powerflow-Briardene Durban North
What is a DPF?
It is a device that is a part of the exhaust system that captures soot or other nasty particles, so that it does not release into the atmosphere.
A DPF can capture up to 85% of the particles released from the exhaust, reducing harmful emissions.
A DPF filter contains a fine mesh light structure that acts like a net; this captures the soot and diesel particulates. Modern DPF filter are made from various materials such as a matrix of porous ceramic material, silicon carbide or metal fibres. Due to the materials and complex design of the filter they can often cost up to R5000 to R25000 from your local dealer. But luckily you get aftermarket DPF filters that you can buy for a reasonable price that works just as good as the original DPF.
How long should a DPF last?
The lifespan of a DPF is very difficult to determine. There are many factors to take into consideration however the DPF for the average motorist should last in excess of 115000km +/- from new. For the occasional city driver this may be considerably sooner due to increased soot levels this is because the engine does not operate at optimal temperatures and generally lower engine speed which results in incomplete combustion.
What does the DPF warning light on my dash mean?
The DPF warning display means that the DPF filter is not working correctly or it is in need of maintenance or regeneration, the DPF sensors or probes monitors the exhaust back pressure and temperature of the system to ensure it is working correctly.
Once the light on the dash is triggered a regenerations process is activated, if the regeneration process is incomplete it is in need of repair or replacement.
DPF warning light and engine/management
DPF warning light will illuminate to notify you that your DPF is becoming blocked and requires regeneration. When the car meets its condition for regeneration it will use either passive or active regeneration.
If the regeneration fails an additional light will appear and that will be your Engine Management Light, this usually occurs when the DPF is beyond the point of regeneration.
NB: When this occurs your car will go into limp mode, this may restrict engine power and revs, resulting in additional misery!
What should I do when I see the DPF warning light?
The process of DPF regeneration would differ, best you can do is to contact your local dealership for advice when the DPF warning light shows.
Failure to correctly regenerate the filter in a timely manner can lead to a costly manual regeneration or in the worst case, failure of the device which leaves no choice but to replace it.
There are different types of DPF regenerations.
- Active regeneration
- Passive regeneration
- Force regenerations
Regeneration is normally controlled by the ECU which automatically kicks in when the ECU reads a build-up in the DPF using sensors, this proses can be repeated until the ECU get a clear signal.
- Engine runs on normal operating temperature
- At least 60 Km/h
- At least 2500 RPM
- Fingers crossed!
It is performed by the ECU triggering a post combustion fuel injection. This increases the temperature in the DPF, Burning off soot and particles that has built up in the filter.
NB: This will cause a higher than normal fuel consumption and increased engine temperature.
Passive DPF regeneration takes place automatically on motorway runs when the exhaust temperature is high. (Many manufactures have moved to using active regeneration as many motorists do not often drive for prolonged periods).
Passive regeneration often uses a DPF additive to help it to be more affective. DPF cleaning additives are a chemical solution to add to the fuel tank. The additive does not increase the temperature of your DPF but decreases the temperature at which the soot will burn off. The additive may assist the DPF regeneration process when the DPF cannot reach its operating temperature to burn off the soot an additive may be a cheap and viable solution to a block DPF but this by no means is guaranteed especially if the DPF is clogged with ash rather than soot, long term use of an additive can increase your fuel costs.
Forced regeneration is a way of cleaning the DPF using a maintenance process. This process can only be started by either a main dealer or a qualified mechanic with the right tools and access to the vehicles management system.
DPF cleaning cycle in the workshop runs the car at a high RPM for a considerable period of time. The ECU injects fuel into the post combustion process to achieve a higher exhaust gas temperature and which ensures that it heats up the DPF filter to an extreme temperature, burning off the contents of the filter. NB: In most cases the engine will need an oil change as the vehicle will literally "cook" the lubricant.
DPF Cleaning is a manual process that removes the soot and diesel particulates from the filter, the main dealer or mechanic achieve this using ultrasonic cleaning technologies in combination with special additives , this process removes all traces of particulate returning it to normal operating functionality.
What can cause my DPF to block?
It's not just your driving habits that can cause your DPF to block. There is a little gremlin sitting under your bonnet that could be the cause off all your headache... your EGR valve.
An EGR valve is a small engine component that recirculates a portion of your exhaust gases back into the engine, over time the EGR valve mechanism can become contaminated this in turn can cause the device to malfunction and not operating on its original design.
NB: A faulty EGR valve that is stuck open will increase the amount of particulates, soot and carbon to be fed into the DPF.
Faulty fuel injectors
Faulty fuel injectors have been flown under the radar when looking at causes of a blocked DPF, a faulty fuel injector can spray excess fuel in the combustion process resulting in unburned fuel that can causes the vehicle to run rich and then resulting in excess soot clogging up the DPF quicker than normal.
Faulty Turbo charger
A faulty turbo charger can cause havoc for modern diesel powered vehicles. Anything to upset the delicate air fuel mixture can cause your diesel engine to belch out even more soot that it already does. A faulty turbo charger can also leak oil into the exhaust system resulting in the DPF being drowned in engine oil.
Can I remove my DPF?
Yes you can, but the removal of the DPF will cause a ECU fault and therefore the services will most likely require the removal of DPF fault reading from the ECU (reprogramming software of the ECU).
We have learned that removing the DPF only works for some vehicles and so does the software; the latest diesel engines are less prone to problems, because the combustion is more efficient so as vehicles are evolving so is our technology and at some point the DPF will be perfected and won't need change or repairing.
Is there a purpose for a DPF
The DPF is in the exhaust system of all diesel powered cars sold new since 2009. The DFP function is to trap particles that are caused by the combustion process and thereby prevent visible smoke into the atmosphere. The DPF will gradually get clogged with soot that gets trapped by the filter, however the car is designed to clean it by heating up the soot turning it to ash and expelling it, this happens often, either when you're travelling or because the ECU initiates it what's known as regeneration.
A general opinion is that the DPF is of a cosmetic nature as it eliminates visible diesel smoke then burns the soot into ash and expels it through the exhaust.
The question then arises, do we really need a DPF when it takes one form off harmful gas and converts it to another harmful substance.
Should you wish to discuss any particular technical issues about your exhaust system we at Powerflow Briardene would gladly oblige. Pay us a visit with your car to enable us to inspect and advise.