Diesel particulate filters are a major source of income for cleaning services like Ceramex, but the emissions-reducing devices can hit drivers hard in the pocket
John Evans
3 February 2019

On an industrial estate in Slough, an enterprising British company called Ceramex is cleaning and refurbishing up to 1000 diesel particulate filters (DPFs) a week for many leading truck and car makers. 

Business is good, says Marcus Beament, its head of sales: “We’re a tier-one supplier to major OEMs who have realised that cheaper cleaning methods are not always the most effective.” 

It sounds like a sales pitch but proof of Ceramex’s success is all around me, not least in the shiny new production line that cost more than £2 million to build and which features the firm’s unique Xpurge system that cleans and returns the used DPFs to near-new condition. 

A DPF’s job is to capture the microscopic particulates, or soot, in a diesel engine’s exhaust. These can clog up the DPF but how quickly they do so depends on things such as whether the engine uses oil with low Saps (sulphated ash, phosphorous, sulphur), the condition of the injectors, glow-plugs, EGR valves and turbo, the complex algorithms overseeing everything and, apparently, the vehicle owner’s style of driving… 

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When the quantity of soot reaches critical levels, it’s burned off in a process called regeneration. There are two types: passive and active. 

Passive regen takes place automatically but only when the exhaust temperature has reached approximately 600deg C, a level usually achieved on motorways and A-roads when a constant engine speed in excess of 2000rpm can be sustained. 

Active regen takes place when the soot deposits reach a limit of around 45%. The ECU triggers post-combustion fuel injection to increase the exhaust temperature. To work, the process cannot be interrupted. Also, because of the amount of fuel it requires, the car must have at least 20 litres of diesel in the tank. 

A downside of active regen is that a lot of unburned fuel ends up in the engine’s sump. It’s eventually burned by the engine but this only adds to the deposits of soot in the DPF. 

During regen, the soot becomes ash, a by-product that is rarely talked about but which can become a problem on diesel cars that have done more than 80,000 miles. There are various ways to rid DPFs of it but, according to Ceramex, the only one that truly works is its unique Xpurge system that uses purified water and air. As proof, it extracts a skip’s-worth of ash and soot every three months. 

So, keep your car in good shape, give it a blast now and then – especially so if most of your driving is of the short, stop-start variety – and when the DPF gets bunged up with ash, get it cleaned. It all sounds straightforward, so why is any discussion about DPFs like opening a can of soot-clogged worms? 

Mitch McCabe, Autocar’s head of video, reported in October last year that his 2018-registered Vauxhall Insignia Sports Tourer with 10,000 miles on the clock had developed a problem with its DPF. 

The first he knew of it was when a message flashed up on the Insignia’s dashboard saying the filter had been unable to regenerate itself. A few seconds later, the car went into limp home mode. The Vauxhall dealer McCabe spoke to said that if the DPF was damaged and his ‘driving style’ was to blame, he’d be liable for the repair bill – a not insignificant £2500 plus £960 fitting. 

“It seems that the manufacturers have the right to decide whether the failure of the DPF is a warranty issue or not, based on your ‘driving style’,” said an aggrieved McCabe. Fortunately for him, the Insignia’s DPF was simply faulty and was replaced at no charge. McCabe was relieved but not entirely happy. “It’s obvious that on certain used cars, the DPF will cost more to replace than the vehicle itself is worth,” he wrote. 

His experience triggered a few tales from Autocar readers who had suffered DPF issues with their cars. They included Julian Fack, owner of a Porsche Macan S Diesel that, since he bought it, has signalled problems with its DPF on four occasions – roughly every 6000 miles. On two of them, it went into limp home mode and required a dealer to carry out a forced regen. 

“There can be as little as a minute between the car alerting you to a problem and it going into limp home mode,” says Fack. “In that time, and assuming you’re on a clear road, you must start the regen process, which involves driving the car at no less than 37mph for 10 minutes with the engine turning at over 2000rpm.” 

Another reader, Nick Wilson, explained how he’d bought a new Land Rover Discovery Sport in March 2017, only to sell it 18 months and 37,000 miles later after it developed an appetite for more frequent oil changes. “The dealer suggested short journeys and my ‘driving style’ were to blame but I travel all over the country so the car gets a good workout,” says Wilson. 

He later discovered the problems had less to do with his driving style and more to do with an oil dilution issue common to some 2016-17 model-year Range Rovers, Discoverys and Evoques

A bulletin sent to Land Rover dealers and headed ‘Early service due to oil dilution’ explains that the ‘service required’ message is triggered by unburned fuel in the engine oil, itself caused by a higher-than-expected number of partial DPF regeneration cycles. 

Land Rover’s solution was to offer owners of the affected vehicles free oil and filter changes but only during the car’s first 50,000 miles. “I feel I was sold a car with a known fault,” says Wilson. “It cost me a lot of money to hand the car back but I’d lost confidence in it.” 

Wilson’s experience highlights the fragile interdependence of today’s emissions control systems. However, according to MotorEasy, a motoring association that provides vehicle warranties, the number of claims concerning DPFs is relatively low. 

“Problems with DPFs aren’t affecting too many vehicles,” says Rory Buckley, marketing director at MotorEasy. “Instead, the attention-grabbing aspect is that when a DPF does go wrong, the repair bill is significant, so prevention is key.” 

Drive a petrol car? You could be next

Don’t think you’ll escape the occasional particulate problem behind the wheel of a petrol car, because gasoline particulate filters (GPFs) are being introduced on these too. 

Volkswagen has been fitting the devices to 1.4 TSI versions of the new Tiguan since 2017 and last year introduced them on the Up GTI. Audi, Mercedes and Ford are among others also fitting GPFs. 

Their hand is being forced by tougher emissions legislation designed to reduce particulate emissions from petrol engines. Although CO2 emissions have fallen on the new generation of small direct-injection, turbocharged petrol engines, particulate levels have been increasing. The result is that an unfiltered GDI petrol engine produces up to 1000 times more particulates than earlier petrol engines and 10 times more than a diesel equipped with a DPF.

Read more

Volkswagen equips petrol cars with particulate filter technology

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Join the debate


3 February 2019

Good to see this article mentioning oil as a big factor in DPF failures. While new car failures were often down to people buying the wrong car a lot of high mileage early failures were down to back street garages filling up the car from the giant barrel of oil that they used in every car that came in. Of course when the s**t hit the fan they weren't going to tell the owner they had been using the wrong oil for 60000 miles. Similar to the issue with fuel pumps breaking up that turned out to be the owner putting petrol in the tank 6 months earlier, realising the problem and shifting it on before the pump broke up.

28 June 2019
It is nice to learn more about this case. Thanks.

28 June 2019

I would love to try DPF out since it is great to give good help.

3 February 2019

My previous car was a dpf equipped diesel, yet despite my driving profile of 500+ motorway miles a week, it was doing active regeneration twice a week. I'd worked out when it was doing them and i always ensured it finished, but thought a warning message or light to say 'regen occurring, do not turn off' would've been helpful for drivers to look after their dpf better.

3 February 2019

I used to have a diesel Focus and it was usually obvious when it was regenerating because it became unpleasant to drive, especially around town. It didn't run smoothly, was hesitant and sounded different. But I can imagine a lot of people would miss these things, especially out of town and like you I've often wondered why there isn't a light on the dash to warn you or even a button to give you the option of forcing a regeneration if you know you going on a longish drive. As for GPFs, I wonder if they will be less problematic because petrols, even direct injection cars, produce less soot than diesels and warm up faster. I guess only time will tell.


3 February 2019

I have always hated the stinking filthy things, and would never entertain one in my drive.

I just dont know why you would saddle yourself with such a potential bag of trouble.

Any savings in cost of fuel are soon absorbed by 11p a litre more expense....DPF and Injector trouble, cost of stinking gut wrenching fuel additive etc.

I dont trust the manafacturers either....they know full well that the emissions tests are creating engines with pretty sketchy reliability/longevity, and are quite happy (as we read here from contributors), to blame 'driving style' rather than face up to their responsibilities.  Its a complete can of worms, made worse by the fact that it is clear that the Government are 'on the case of Diesel and are going to tax it into oblivion....having previously ignored all previous expert opinion and forced everyone into diesels in the first place.

Frankly you couldnt make up such rank incompetence, and god knows why you would want to get involved in this maelstrom of contradictions.

3 February 2019

1 I've run diesels for 15 years with no problems.

2 How were people 'forced' into them. You admit you never owned one.

3. No one bought them for environmental reasons. People started hearing from neighbours about the savings on fuel due to the better economy and biubou them to save money.

4. There is zero chance of any UK government having the balls to take on the motoring lobby ever which is why I went diesel again and will probably do so next time.

3 February 2019

 So, it’s down to the Car owner?, Car makers have had decades to improve DPF Filter systems, should be by this time full proof, but, when it goes wrong and your Garage cuts the umbilical, you could be left with a huge Bill for something that really wasn’t your fault, is there a get out clause in the owners manual for Car makers...?

Peter Cavellini.

3 February 2019

It's a component with a finite lifespan like any other component. If you don't look after it it's going to fail earlier.

3 February 2019

and increasing purchase of EVs


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