A personal viewpoint by Anthony Smith, Director, MediaTechnical Ltd

A year ago if I’d been asked this question, my response would have been an undoubted ‘yes’. Now though, personal experience leads me to worry that things are not as they should be within the dealer networks; that we have perhaps gone too far down the pathway of allowing warning lights and ECU codes to be the primary factor in fault tracing. For largely isolated components such as tyre pressure or fluid level warnings, blown bulbs and so on, this abstract/reductionist approach is fine. But with highly complex systems such as diesel aftertreatment, I believe that reading ECU fault codes should be just the first step in investigating and analysing the root cause of a failure, particularly for older or higher mileage vehicles.

Diesels are increasingly complex in terms of the aftertreatment technologies fitted to them, and problems may express themselves as symptoms that appear remote from the original root cause. For example, even a fault on the engine or intake such as say, a stuck EGR valve, failing fuel injector or an air leak from an intercooler, can negatively impact the ability of the aftertreatment system to do its job properly. In such a case, the aftertreatment warning code can be merely a symptom of the fault rather than a direct indication of its cause.

With dealership-based maintenance and fault tracing appearing to be so heavily reliant upon the reading and interpretation of ECU codes these days, however, there surely must be an increasing risk that the root cause of problems can go unresolved for a long time. This is not such an issue in the early years of a vehicle’s life, but can become increasingly problematic as they age and a vast number of different components wear out, and at different rates that are difficult to predict.

This situation is far from ideal for the customer or for the environment.

Key differences between Euro 5 and 6
The introduction of Euro 5 regulations in 2009 effectively mandated the use of a Diesel Particulate Filter (DPF), and these have proven highly effective in reducing diesel particulate matter (PM) emissions from new diesel cars to almost zero. To allow the DPF to function, an oxidation catalyst is used which converts NO into NO2, a harmful pollutant in its own right but one which is needed for the DPF to function, by allowing the particulate to burn-off at a lower temperature than would otherwise be available within the exhaust system. While some Euro 5 vehicles were equipped with NOx aftertreatment to significantly reduce NOx output as well as PM, this was only effectively mandated for all new diesel vehicles from Euro 6 onwards.

The advent of the WLTP process including the requirement for ‘Real Driving Emissions’ on urban, rural and motorway driving will, I believe, help to ensure that new diesel cars are as clean on the highway as their showroom stickers imply, subject to a mandated allowable conformity factor. But what guarantee to we have that this will be the case throughout a vehicle life of up to, say, ten years or more? The ultimate line of defence is in this respect is the ability of the dealer networks to trace and rectify faults – and here I worry that they might not be as good as they should be.

DPF problems increasingly common – but removal should never be an option
A quick Google search on something like ‘DPF problems’ will very quickly return tales of woe from almost all brands of recent diesel car. In many cases these dissatisfied customers will be struggling with issues that the main dealers have tried and failed to resolve many times over, replacing part after part at great expense and yet still not tracing the root cause of the problem. It will also probably return some offers to remove DPFs and re-map engines to operate without them. Thankfully this is now illegal within the UK, but this doesn't seem to have stopped the service being offered commercially. As the MoT test only provides for a visual inspection for the presence of a DPF plus a comparatively rudimentary smoke test, the latest approach seems to be to remove the filter elements but leave the housing in place. Apart from its in my view very dubious legality, removal of the functional parts of the DPF represents about the worst possible outcome environmentally, with high levels of NO2 emitted from the still present oxidation catalyst but without any benefit in terms of reducing engine-out PM emissions.

DPF problems – or just an indication of problems elsewhere?
In a vehicle in perfect working order, the most likely cause of a DPF full code – triggered when back pressure across the device reaches a pre-set limit due to excessive build-up of soot – is likely to be when it’s been driven exclusively at slow speed around the urban environment. In these conditions DPF regeneration, the process through which the stored carbon is burned off harmlessly, is unlikely to take place as the exhaust temperature is too low. The cure for this is simple: take the car for a high speed spin for 30 minutes or so to trigger an active regeneration cycle, and the problem goes away.

But what if the warning light only appears at high speed ON the motorway? This is something that seems to be pretty common in older vehicles if my Google search is anything to go by.

Let’s just say, purely hypothetically, that when this occurs, your dealership recommends replacement of the pressure sensor. But if that doesn’t work, perhaps on the next visit, they’ll recommend replacing the DPF itself. If this happens, just make sure you’re sitting down when they tell you the price!

Let’s also say that at this point, far from going away, the DPF fault codes are just increasing in their frequency. What do you do now? It’s possible that only after having pretty much replaced the entire DPF system that your dealership might look upstream. So let’s say they find an air leak – somewhere like the intercooler. Now that’s going to be expensive, but if it needs fixing what else can you do but pay up for it?

Only the DPF codes keep coming. So what does the dealer recommend next? Well when they’ve pretty much inspected the entire intake and exhaust system, so perhaps now they’ll look at the engine itself, the injectors maybe? At last, the Eureka moment: a couple of them are on the way out. Chances are that the car has been blowing so much smoke internally within the exhaust, the DPF has been working overtime to clean up all the PM.

All of the above has taken around 8 months, around 5 visits to the dealer, and the best part of £2k in parts and labour. And that’s only if you’re really lucky and they take pity on you and heavily discounted some of the parts cost and a huge amount of their labour too.

Surely such a scenario couldn’t happen? Well it did – to me, between June 2015 and April of this year on a Euro 5 diesel car.

What needs to happen?
My reason for not mentioning the dealer or vehicle brand in my story is because I genuinely believe they did their level best to help me solve the problem – and put a lot of their own time and money towards this endeavour. They’re nice people and they produce great cars – I just won’t be troubling them (or anyone else for that matter) for a diesel car in future. While I still love the driving feel of a diesel and believe that the latest Euro 6 models really are very clean in terms of NOx and PM emissions, I just can't take the risk, hassle and cost of poor aftertreatment system reliability through the second half of the vehicle's life. 

What my experience does show in wider terms, I believe, is that as diesel aftertreatment becomes more complex and systemic in its operation, effective maintenance for the second half of a typical diesel car’s life is an increasing challenge. Fault codes may – as my experience shows – sometimes just provide an indication of the symptoms of a problem rather than its root cause. 

Dealer networks seem to me to have become seduced by the simplicity and ease of use of fault code analysis, and it works really well for new cars or those less likely to exhibit such systemic problems. But if automakers and dealerships are to step up to the challenge of maintaining the aftertreatment systems of an ageing fleet of Euro 5 and even more complex Euro 6 diesels, I believe they’ll need to rediscover some of the practical diagnostic skills of old, and use these alongside the now ubiquitous fault code analysers.

And if they don’t rise to this challenge? Well, my guess is that it will only be a matter of time before we see a dip in diesel car sales as the second hand market falls out of love with their supposed long-term reliability.  In my view it would be a real shame if all of the technical and engineering efforts committed by the auto industry in ensuring that the latest generation of Euro 6 vehicles is clean in terms of both PM and NOx both on-highway and in the laboratory, were to be undermined by this apparent weakness of the service sector.