Diesel Particulate Filter (DPF)
This fact sheet has been put together by Chip Tuning to inform our readers on the problems associated with vehicles fitted with DPF’s even whilst in factory standard trim. (IE NO CHIP INSTALLED)
We have received a few enquiries regarding vehicles fitted DPFs (namely late 2007 -2010 Nissan 2.5 CRD and Mitsubishi 3.2 litre NS Pajero etc). The enquiries suggest a misunderstanding by the vehicle’s owner of how the factory fitted DPF functions, and the associated obnoxious smells or smoke that may result.
We believe the main issue arises from poor, or at best limited, information given by the vehicle manufacturers.
Changes to new car emissions legislation scheduled in 2009, the so-called “Euro 5” standards, will make particulate filters as commonplace in diesel car exhausts as catalytic converters are on petrol cars.
DPFs are used by a number of vehicle manufacturers to reduce the amount of harmful particles released from their modern diesel vehicles. Although extremely effective in most situations, they are not suitable for drivers who do not have the opportunity to drive their vehicle at over 80km/h on a fairly regular basis.
The goal is an 80% reduction in diesel particulate (soot) emissions but the technology’s not without problems – Automotive Service Providers (eg NRMA, AMA etc) are already being called to cars with the particulate filter warning light illuminated (indicating a partial blockage).
It’s clear that changes to driving style may be required too for maximum benefit from these systems.
What is a DPF?
A DPF is a soot, or particulate matter filter for diesel engines. They are used to reduce the exhaust emissions as required by many governmental emission legislative bodies. DPFs are becoming more and more common on diesel engines.
How do they work?
Diesel Particulate filters (DPF) or ‘traps’ do just that, they catch bits of soot in the exhaust.
As with any filter (think of the bag in your vacuum cleaner) they have to be emptied regularly to maintain performance. For a DPF this process is called ‘regeneration’ – the accumulated soot is burnt off at high temperature to leave only a tiny ash residue. Regeneration may be either passive or active.
Passive regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. Many cars don’t get this sort of use though so manufacturers have to design-in ‘active’ regeneration where the engine management computer (ECU) takes control of the process.
When the soot loading in the filter reaches a set limit (about 45%) the ECU can make small adjustments to the fuel injection timing to increase the exhaust temperature and initiate regeneration. If the journey’s a bit stop/start the regeneration may not complete and the warning light will illuminate to show that the DPF is partially blocked.
If you ignore the light and keep driving in a relatively slow, stop/start pattern soot loading will continue to build up until around 75% when you can expect to see other dashboard warning lights illuminate too. At this point driving at speed alone will not be sufficient and the car will have to go to a dealer for regeneration.
How is the DPF cleaned and what is DPF “regeneration”?
A DPF filter can hold a certain amount of soot, but not a huge quantity, so it needs to regularly go through a process of cleaning itself or “regeneration” in order to clear out the soot and allow the vehicle to operate properly. Regeneration occurs ONLY when the filter reaches a sufficiently high temperature allowing the soot to be converted to a much smaller and less harmful by-product, ash.
To allow the filter to automatically regenerate, the engine has to be used regularly at a sufficient engine speed, to ensure a high enough temperature of the exhaust gas. The engine must be under sufficient load to ensure that the exhaust gas temperature is naturally raised. Although it may vary from manufacturer to manufacturer, typically a vehicle must be driven at 80km/h or above for at least 20 minutes in order to automatically regenerate the filter. During the regeneration phase, high temperatures in the filter may cause a slight smell, especially during the first regeneration. Many people would have smelt and complained to the manufacturer about this.
What happens if it doesn’t regenerate?
If the vehicle is not driven in a way that automatically regenerates the particulate filter, it will build up an excessive amount of soot, which, if not resolved, will reduce the performance of the vehicle and damage the filter.
If the filter does build up too much soot, a vehicle warning light will appear to alert you. The problem can usually be solved by allowing the filter to automatically regenerate until the warning light goes out – i.e. by driving the vehicle at 80km/h or above for at least 20 minutes. Check the vehicle handbook for specific guidance on a particular vehicle.
If traffic conditions and speed limits do not allow the vehicle do be driven so that the filter regenerates, it will have to be returned to a dealer for a forced regeneration in order to clear the filter.
If the warning light is ignored and the vehicle is driven without regenerating the filter, it will cause damage to the vehicle, which may not be covered by the vehicle manufacturer’s warranty.
How the vehicle manufacturers get away with not offering warranty on their failures is most concerning to the writer! Seems like the only cover some owners are going to see from their manufacturers is when they cover their own ass!
In some active DPFs active cleaner is made by injecting diesel through an extra injector placed prior to the DPF. These active type DPFs run into their own issues. Problem has been identified whereby stop / start deliveries, for example, will never allow the system to complete the regeneration cycle. When the truck is started again the active DPF system re-institutes an active regeneration and if this happens again and again the catalytic convertor and or the DPF can pool the unburnt diesel within and can actually at times be seen coming out of the exhaust. Warning lights by this stage will come on and a very expensive DPF repair is on the cards. Not a cheap exercise.
Can I fit a full after-market exhaust to these vehicles with DPFs?
We suggest not to as the less restrictive aftermarket exhaust may have an effect on the exhaust temps (lower) and make the factory ECU inject more fuel than what is needed. This causes white smoke on cold starts. This is certainly true with Nissan D40s and will apply to other vehicles as well. Chip Tuning ECU reprogramming warranty does not cover white smoke in this situation. Our advice: Save your money and when the time comes, just replace the factory DPF with our DPF delete pipe and allow us to reprogram the factory ECU. Leave the rest of the exhaust as is.
Which drivers should order vehicles with DPFs?
A vehicle fitted with a DPF is suitable for all drivers who have the opportunity to regularly follow the procedure that is detailed in the vehicle handbook to allow their filter to automatically regenerate – i.e. driving at a sufficient speed for a sufficient amount of time. In these circumstances, a particulate filter significantly reduces the harmful emissions of the vehicle, and except for extra fuels used for regeneration, they provide this with absolutely no adverse effects to performance or maintenance.
We recommend that drivers who only use their vehicle for urban journeys may be better looking for a diesel without DPFs fitted.
Vehicles with DPFs
The majority of new diesel vehicle manufacturers now have DPFs as standard fitment, but not on all diesel models. For specific details of individual models, please refer to manufacturers’ websites.
Check the handbook
If you buy a car with a DPF fitted it’s important to read the relevant section of the vehicle handbook so that you understand exactly what actions to take if the warning light illuminates and how, if at all, your driving style may need to be adjusted to ensure maximum DPF efficiency and life.
Alternatives for urban drivers
If a driver is restricted in their ability to regenerate a DPF through driving, i.e. driving in a lower gear with higher RPMs, there are other vehicles that can be chosen, which do not use this technology. Some models come in vehicle derivatives with and without a DPF, so the derivative without the filter, typically with a smaller engine, can be chosen and again the Chip Tuning Diesel Performance Solution Module will help in powering-up these lower powered engines.
Chip Tuning’s own experience
Personally, we’re also seeing some limited evidence of DPF”s failing to regenerate, even on vehicles used on motorways. On the Director”s own NS Pajero, Mitsubishi recalled the vehicle model no less than 3 times to reflash the ECU with a “better” regeneration parameter. The latest reflash managed to keep the DPF light from illuminating. During one of these recalls however, the catalytic convertor and the DPF were replaced under warranty WHILST AFTERMARKET PERFORMANCE PRODUCTS WERE FITTED. It seems Mitsubishi at least, are doing the right things by their customers. Well done MMA!.
We believe cars with a very high sixth gear (or overdrive) the engine revs are too low to generate sufficient exhaust temperature. Occasional harder driving in lower gears should be sufficient to burn off the soot in such cases. Chip Tuning Diesel Performance Solutions Modules may actually help in supplying a hotter exhaust by supplying more fuel thus burning the particular matter.
What the long term effects this ,,exhaust filter re-generation” may have on Engine Life is yet to be seen. If better technology occurs from this, all well and good however in the mean time we believe the public has a right to know WHAT THEY ARE GETTING FROM MANUFACTURES. AFTER ALL, IT IS OUR MONEY!
NB, Our 30 day warranty will set you mind at ease and afford you the right to return the Chip for a full refund if your vehicle does not happily operate with the Chip Tuning upgrade. Do please give us the opportunity however to assess any other reasons for the issues. You may find we have a way to address or work around the problem and get you to enjoy the power increases as you should do.
ADDENDUM: The first edition NT Pajero had a larger DPF fitted and this no longer had sensors installed front and rear. This model Pajero will conduct a POST BURN INJECTION clean once every 300 – 400 kms and no longer look at whether the filter is blocking up during the interim. The larger free flowing DPF allows this.
However, Mitsubishi may have had enough of customers deserting the brand that the latest model (version 2) NT Pajero no longer has a DPF AT ALL. (This is the same for the Nissan D40.) (
update: new models have had to re-instate the DPF to pass current stricter emission laws))
If you wish to know how the power is increased in these models over the NS, just look at the freer flowing exhaust. We give a sneak preview of freer flowing exhausts in our Nissan Navara write up.
See this Good Explanation of the DPF System: