Diesel Particulate Filter Problems

A search of any search engine for “Dpf problems” or “Dpf blocked” will quickly bring up thousands of tales of woe in relation to owners having problems with the DPF’s on their cars, in fact the problems have been so widespread that in 2011, the whole Dpf issue was subject to a BBC Watchdog program – A UK based consumer TV program. Unfortunately, in the years which have followed the whole DPF reliability issue is still very much with us an doesn’t seem to be going away.

The main issue with DPF’s seem to be related to them blocking, which isn’t unusual due to the fact that they are designed to trap soot particles which would otherwise be discharged into the environment. Unfortunately, enabling the DPF filter to regenerate (clean) itself, requires taking the car on regular motorway trips at constant speeds – something which is difficult and expensive to do on today’s congested roads, and expensive fuel prices.

With diesel fuel costs at an all time high, taking the car on a motorway trip for no other purpose than for a component to clean itself is often not a viable or welcome option for most owners, and so it gets overlooked, to the point where the DPF becomes blocked and a dashboard warning light illuminates on the Dashboard. This is the point where, if left ignored, it can get very expensive very quickly, often with manufacturers failing to honour repair or replacement under the vehicle warranty, usually due to the excuse that the issue occured because of the owners’ driving style.

The dashboard light illuminating, is an early warning that its time to take the car on that motorway drive, whether you are planning a trip or not!. If you ignore this warning light and don’t allow the DPF to regenerate than it is more likely to require the attention of a dealer in the near future for a forced regenerative cleaning and this can cost anything between £100 and £250 per clean. Worse still, the DPF can reach the point where it has gone beyond cleaning and require a complete replacement, and this can cost up to £3000.

Prevention is always better than cure, and so if you own a Car with a DPF then you should not use it for routine short journeys or typical school runs, and its probably wise to avoid diesel cars altogether unless you do over 10k miles per annum, and most of that out of town.

If your use of the car only routinely involves urban road speeds and a lot of stop-start town commuting, then you really should make a point of taking the car for a longer drive at least on a fortnightly basis, or better still avoid a diesel car for anything but long journeys.

At least one car manufacturer has issued a statement that they will not honour any warranty claims involving a DPF replacement if it is believed that the car has been used outside of their recommended guidelines – i.e the car is used for short journeys and the owner ignored the DPF early warning light.

Other problems relating to the DPF include the oil level rising within the sump, to the point where it causes damage to the engine, or the engine effectively runs away (uses its sump oil as a fuel) to rev to its destruction. This happens when fuel is injected into the DPF unit in order to instigate and fuel a regeneration burn off, and the regeneration fails resulting in the unburnt fuel being dumped into the sump.

On some cars, the existence of the DPF can actually increase the fuel consumption of the vehicle, especially in those which have a fuel based catalyst regeneration system where fuel is used to ignite and burn off the trapped soot particles. MPG figures can drop significantly during regen cycles.

Its also quite worrying that there are forum threads relating to owners’ whose cars have burst into flames because of a DPF related incident. One such forum discussion, can be found Here

The DPF unit can sometimes be damaged by an incomplete regenerative cycle, i.e the car stops or enters traffic so the regen procedure cannot complete. Since there is no obvious indication of a DPF regeneration procedure underway, it is virtually impossible to know on some cars when it is taking place. Thus the procedure may be interrupted by the driver unwittingly, and damage or blocking resulting.

There have been reports of various sensor problems on the DPF unit, which again require the attentions of the dealer and possibly more expense.

Cars fitted with a DPF unit should not be parked over long grass or other combustible materials, as the outer unit can get extremely hot after a regeneration process and can ignite materials nearby.

Of course the main drawback of owning a DPF equipped car, is the ongoing requirement make needless semi-regular motorway or A-road (highway) trips, for no other reason than general preventative maintenance or because a light on the dashboard told them to do so. Obviously if part of your daily commute requires a motorway trip or you drive up the motorway every weekend, then this will not be a problem.

But for those whose commute involves the stop-start traffic jam of urban roads, or for those cars and vans used for Taxi’s, Driving Instructors Cars or Delivery Vans, then the DPF blocking is more likely to raise its ugly head sooner, rather than later.

Even a working and looked after DPF unit is likely to wear out and need routine replacing eventually with some manufacturers listing this as becoming likely at as low as 90k miles, and this requirement will lead to low residual values on second hand cars. After all, would you want to buy a four year old car, with 80k miles on the clock, knowing that in 10k miles time, you would need to pay upto £2000 to replace the DPF unit?. Cars are also likely to be scrapped much sooner, when they reach the point where replacing a worn out DPF is likely to cost more than the actual value of the car.

2 Responses to Diesel Particulate Filter Problems

  1. Bill says:

    Hi,

    Have you heard of any dpf problems with the Honda 1.6 dtec? I understand it is one of the first engines designed around a dpf; locating the filter next to the engine block for easier regen. Two different Honda dealers have said they’ve seen no problems with this engine.

    Thanks for any help you can give me.

  2. admin says:

    Hi Bill,

    I have no experience of this engine personally but a quick search of google brought up the following thread https://hondakarma.com/threads/1-6-i-dtec-dpf-blockage.183587/live?page=1

    There is also a report on the Honest John site in relation to a 1.6 Civic needing a new DPF, although driving style (short journeys) played a part in this, which does show that the new system still doesn’t make it suitable for all driving styles, and the usual DPF advice about avoiding short journeys would still apply.

    https://www.honestjohn.co.uk/carbycar/honda/civic-2012/?section=good

    Putting the DPF closer to the Engine certainly helps, but it still relies on the Engine and Exhaust Gas temperatures reaching, and being maintained at the upper level in order to naturally burn off the soot which has accumulated and this may be difficult to achieve consistently enough to keep the soot loading below the level required to avoid a full regeneration unless the car is used for long journeys at constant speeds on a regular basis, and even then with roadworks and stop-start traffic, it may not entirely prevent the DPF blocking eventually.

    If anything the advice on this blog (and elsewhere) to take the car on long journeys on a regular basis actually applies more to this type of Regeneration than to the earlier type, largely because it relies on heat from the engine exhaust gases to heat the DPF catalyst in order to burn off the soot whilst on the move. On a Diesel car it can easily take 15+ miles of steady driving for everything to become hot enough for this process to begin.

    As strange as it sounds, as Diesel Engines become smaller, and more efficient, its actually going to get harder and harder to produce the levels of heat for this kind of regeneration, as obviously a more efficient engine produces less waste heat!, witness how long it takes for the heater in a diesel car to get warm on a cold morning, hence why a lot of manufacturers fit Auxiliary Heaters to warm the coolant up quicker so the cabin heater warms up quicker!. Although of course this additional heater doesn’t help the exhaust gases to clean the DPF.

    So, with this kind of design your chances of a DPF blocking are probably reduced, (assuming you do the kind of journeys where the Engine gets hot enough to continuously burn off the soot naturally), however if you only do short trips where the car barely gets up to its normal operating temperature then the new system of regeneration probably isn’t going to help much, and certainly won’t avoid the car to carry out an active regeneration periodically. Regardless of what the dealer tells you, I would still heed the same advice as applies to any DPF equipped car, e.g avoid lots of short journeys, avoid supermarket fuel, also ensure that the car gets the proper LOW SAPS oil formulated for DPF cars every time its serviced, and you would be as well to change the oil at least every 8k miles, which is good advice on any Diesel car. I would also take some time to read what the owners manual for the car says in relation to its DPF as well.

    The only time I will be convinced that there is a foolproof & reliable DPF system which is suitable for ALL driving styles, is when the dealer / manufacturer covers all failures under warranty, and gives a decent warranty on the DPF without any clauses on driving style!.

    Incidentally this is Honda’s own advice page on the DPF system

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