Alternatives to Replacing a Blocked DPF

Whether this is the first time that you have seen the Diesel Particulate Filter warning light illuminate or if you are getting the DPF Dash Light appearing on a regular basis, then in a lot of cases driving style and how the car is used, and the annual mileage are probably all in someway to blame. Unfortunately the appearance of the Diesel Particulate Filter on all new diesel cars, has effectively excluded them from being used for short journeys or city driving, and so if these are the types of journeys that you are making or intending, then you really need to re-evaluate your usage or buy a petrol (Gas) powered car.

Modern diesels with Diesel Particulate Filters are now only recommended for drivers covering at least 12k – 15k miles per year on regular motorway (highway) trips in order to maintain their Exhaust filter systems. Failure to use the car on the recommended regular long journeys results in the continued blockage of the Diesel Particulate Filter, to the point where it needs replacing, and they don’t come cheap!. Worse still, a blocked diesel particulate (DPF) can cause additional problems such as poor fuel economy and even premature turbo wear and failures.

But what if you are getting Diesel particulate filter (DPF) Problems, and you do drive the recommended annual mileages and follow the instructions of the manufacturer?, what happens if you have already attempted a DPF cleaning procedure and the warning light still remains? well these instances are not as rare as you would imagine and it is all down to the factors programmed until the vehicle ECU computer which are required to create the perfect set of running parameters for the DPF to regenerate (clean itself).

The Diesel particulate filter (DPF) regeneration cycle only takes place when a certain set of criteria is met, and these parameters include engine and oil temperatures, vehicle speed, vehicle rpm and more importantly – EGT (Exhaust Gas Temperature). In most cases the EGT has to be around 250c before a DPF regeneration can be preformed, and for the EGT to reach these levels, the car has to be in excellent condition mechanically and everything else in the chain needs to be working correctly and be in good order, including some components which you may think, have nothing to do with diesel particulate filter regenerations!.

So the reason your Diesel Particulate Filter may continually become blocked to the point where it needs professional cleaning or even replacement, or the fact that it refuses to regenerate in the normal way could easily be due to a failed component or soot blockage elsewhere. The main reason why the EGT may fail to reach the correct temperature level for DPF regeneration is down to a component called an EGR Valve, this component controls air and exhaust gases into the intake manifold, and often becomes blocked with oil residues, carbon and soot, which solidify and jam the valve in one position or block the flow of gases completely.

So before paying thousands to a dealer in order to replace your blocked Diesel particulate filter (DPF), first investigate that there are no underlying reasons elsewhere as to why the Diesel particulate filter became blocked in the first place as a DPF becoming blocked to the point of needing to be replaced is usually due to it seemingly being unable to regenerate itself normally after several normal attempts.

I’ve listed the individual components to check below, as their own demise can directly cause a repeated failure of a normal programmed particulate filter regeneration, and it wouldn’t be unusual for more than one of the list below to have failed, especially on an older or high mileage vehicle.

EGR Valve – Precisely controls the flow of air and exhaust gases into the intake manifold. EGR Valves are well known for being problematic due to sticking and blocking over time from solidified carbon and soot deposits. EGR Valves were a huge problem even before Diesel particulate filters (DPF) were fitted, and now when they block they can cause a domino effect, lowering the EGT and so preventing every particulate filter regeneration attempt. Some EGR valves are cooled by the Engine coolant, and these can contain thermostats which also stick or fail.

Glow Plugs – On some vehicles, the glow plugs are activated during a DPF regeneration cycle, failure of one or more glow plugs or their electronic controller can prevent a DPF regeneration

Thermostat Sticking – An engine coolant or EGR thermostat failing can cause erratic engine temperatures, which result in one of the required parameters failing to be met (Engine Temp)

Coolant Temperature Sensor Failure – Similar to above

Lambda Sensor Failure – Part of the emissions system and whose failure can directly cause a Diesel particulate filter (DPF) regeneration to fail.

DPF Pressure / Back Pressure Sensors – a DPF Unit itself may also have several pressure sensors attached to its body which monitor and control its operation, and these can also fail, as can temperature probes located in the exhaust system, often these will give false readings which may lead to the DPF being incorrectly condemned at a garage – an expensive misdiagnosis!.  In fact instances of failed DPF pressure sensors are far more common than failed DPF units, and so checking these with a handheld fault code reader should be high priority.

Diagnostic Fault Code Reading – In order to fault find all of the possibilities above will require the car to be connected to a diagnostic system – sadly a lot of garages will just automatically take a DPF failure at face value and not know or bother to investigate an underlying cause or will risk giving a misdiagnosis caused by incorrect readings from a failed DPF pressure or lambda sensor, and will instead just tell you that a car needs a new particulate filter without checking out any other (cheaper) possibilities first, and so checking the car yourself for stored fault codes with a basic handheld diagnostic code reader is a cheap and effective way of establishing any underlying problem or faulty lambda or DPF sensor before the car is taken to a dealer where a misdiagnosis could easily land you with a four figure bill for a needless DPF replacement.

There is no magic wand which can be waved in relation to diagnosing DPF related faults, but good all ’round maintenance can be crucial to preventing them occurring in the first place or a repeat of it happening in the future. Suffice to say that a good clean of the EGR Valve, Intake Manifold and regular oil changes (with suitable low ash oil) will prevent the DPF from blocking again, and if done early enough as an extension of normal regular service intervals, may even stop it occurring in the first place.

So, once you have identified and repaired any underlying cause of the DPF Blocking in the first place and the warning light illuminating, how can you save your terminally ill DPF and return it to working condition without paying the dealer a fortune for a new one?.

First, try a normal regeneration, add a bottle of Wynns DPF Cleaner to a 1/4 tank of premium diesel (Shell V-Power / BP Ultimate etc) which together will both help to increase combustion and EGT temperature. Drive the car normally until it has reached its normal operating temperature and then go for a motorway or dual carriageway drive, choosing a low  gear in order to keep the engine rev’s comfortably at 3000 rpm and the vehicle speed above 45mph – drive this way for at least 25 minutes.

If this doesn’t produce a regeneration, and if the warning light is still illuminated then you may need to carry out the steps below.

(A) Take the car to a dealer or independent garage and ask them to perform a manual emergency regeneration, this should cost between £100 and £250 depending on the dealer. However, if this fails or they tell you that the DPF is blocked and requires replacement, then you should consider the additional advice below before committing to a replacement.

(B) if you feel brave enough to tackle working on a car yourself, then taking off the DPF filter and cleaning it yourself with a jet wash or similar can also remove the excessive soot inside, or reduce it to the point where an automatic regeneration can take place once it is refitted. However this relies on having the experience to find the DPF and the tools and ramp available in order to access carefully remove the DPF in the first place, although some high street garages should be able to do this for you, for an hour or two in labour costs.

(C)  There are specialist DPF cleaning companies who can remove and clean out the DPF using special cleaning additives, and depending on the method, it can be carried out with the DPF on or off the car. Whilst this cleaning will cost around £300 – £400 it is still a fraction of the cost of replacing the actual DPF unit.

Once your DPF has been returned back to a healthy state, you should drive the vehicle in accordance to the owners’ manual, only use premium Diesel fuels such as Shell V-Power or BP Ultimate and also routinely add Wynns DPF Cleaner to every tank of fuel. It’s also a good idea to carry out the additional servicing maintenance in relation to cleaning the EGR Valve every 20k – 25k miles.

Oil quality is also very important on any Turbo Diesel car, especially one with a DPF system and so I also recommend changing the oil every 10k miles using the correct grade of low ash (Low SAPS) oil. This should hopefully prevent further DPF related problems returning at a later date and allow your DPF to continue to function to the end of its design life cycle (90k – 120k miles).

If you only drive short journeys or live in a congested City or Town Centre then its a good idea to swap the Wynns additive above, for a high grade commercial additive used in Buses and Taxi’s. The CDTI Platinum additive is very expensive, but is extremely effective in making the engine burn cleaner and so reducing the level of soot entering the DPF itself, meaning it can go for far longer without having to re-generate. The additive is very effective, having been designed for City based diesel vehicles in low emission zones, it is also expensive, but the 1 litre bottle will last for a very long time, and prevention is much cheaper than regular professional cleaning or eventual DPF replacement.

If the Diesel Particulate Filter has reached the stage where it is damaged or cannot be regenerated or has reached the end of its designed life cycle (at 90k – 120k miles) then it will need to be replaced. Avoid expensive dealer particulate filter replacements, and settle for an aftermarket alternative, many of which can be obtained for a more affordable £250 – £400. Links to aftermarket diesel particulate vendors, can be found on our DPF Aftermarket Page.

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