Motoring advice: Diesel cars and the dangers of ignoring dashboard warnings

If you’re driving a diesel vehicle, it’s likely that a filter has been added to reduce harmful emissions. But while these filters can cause all sorts of problems for your car, it’s dangerous to ignore them and usually illegal to remove them.

By Ben Metcalfe, XLCR Vehicle Management.

So how can you live in harmony with your filter? Diesel Particulate Filters have been effectively required on the exhausts of new diesel vehicles since 2009, when the Euro V standard came into force. Many cars registered before 2009 will have had one fitted in anticipation of the change in standards.

DPFs do exactly what they say: they catch bits of soot in the exhaust. As with any filter, they have to emptied regularly to maintain performance. For a DPF, this process is called regeneration, which should occur in the course of normal driving. If not, it should be possible to complete a regeneration cycle and clear the dashboard warning light by driving for 10 minutes or so at speeds greater than 40mph.

If unsuccessful, the extra fuel injected into the cylinders will not burn and the oil quality will deteriorate and its level will rise. It’s important to check the dipstick, as diesel engines can run on their own oil if the level is excessive — often to the point of destruction.

If you ignore the DPF warning light, soot will continue to build up, at which point you can expect other dashboard warning lights to come on and you will need to take the car to a dealer for "forced" regeneration.

Continue to ignore warnings and soot loading keeps increasing, then the car will not run properly and the most likely outcome is that the DPF will need replacing. This costs at least £1,000 plus labour and diagnostic time.

The most commonly-fitted type of DPF has an integrated oxidising catalytic converter, which requires an additive that will require replenishing at some point in the car's life. It is absolutely essential that this tank is refilled as without it, regeneration is unlikely to be successful and a new DPF may be needed.

Some companies advertise a service to remove your DPF and reprogramme the engine management software. However, it is illegal to use a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet, and removal of a DPF will almost always contravene these regulations. This procedure may also invalidate your insurance and will likely see your vehicle fail its MOT.

Even if your driving isn't mainly urban/stop-start, changes to driving style may be required to keep the filter systems working. In fact, if you're buying a new car and plan to use it mainly for town-based, stop-start driving, you may want to avoid a diesel car fitted with a DPF, because of the hassle.If you’d like to know more, or you’re shopping around and want to consider the alternatives, we can help. Established in 2000, we’ve built the best-value contract hire and leasing company in the country with more than 20,000 vehicles on the road. We’ve got a 98 per cent customer satisfaction rating across both business and personal customers - so we’re happy to help you select your next vehicle.