Restricted driving ranges can create expensive problems for owners of diesel cars, if they're not careful.

Owning a diesel car can have its upsides but diesel cars are not designed for low mileage driving. They are at their most efficient on long journeys and have particular problems when being driven on short journeys at low speeds. And with many journeys limited to two kilometres at this time, it means many people are driving in exactly that way.

The main problem that can arise in these circumstances is usually with the diesel particulate filter (DPF).

These filters need to be unclogged and drivers who do low mileage often tend to have to take their cars on to a motorway for up to an hour at relatively high speeds to de-clog them after the DPF warning light comes on. That can't be done these days, however. So, in order to avoid expensive repair and replacement costs, people need to be mindful of the orange warning light that comes on on the dashboard when the DPF is clogging. Drivers should check their owners' manual to identify the appropriate light on the dashboard.

If someone continues to drive for shorter distances the orange warning light may alter to red and then you have a problem. A red light signifies a real problem and you should stop driving the car altogether. Whether you continue driving short distances with an orange light is a judgement call. If you are doubtful, get expert advice.

Replacing a DPF can cost over 1,500 Euros for the part, before labour costs are added.

DPF's can clog easily if only used on short journeys at low speeds.

LeasePlan, the vehicle leasing company has previously compiled the following list of frequently asked questions about DPF's':

Does my Vehicle have a DPF?
In 2009 the "Euro 5" emissions standard was introduced by the European Union. To meet the emission requirements a DPF was necessary for diesel engines. Many manufacturers introduced the DPF in anticipation for the "Euro 5" requirement so DPF's can be found on many diesel cars from 2006 onwards.

How does a DPF work?
The DPF filters pollutants through small fibres within the housing. When the DPF is full it goes through a cleaning phase known as "Regeneration". The vehicle's computer determines when to regenerate the DPF based on the amount of soot/particulate matter in the filter.

The engine computer will raise exhaust temperature by altering engine timing and fuel injection quantity. This raises the temperature in the DPF to circa 650c and burns the trapped soot/particulate matter to ash.

What does the DPF warning light mean?
This is indicating your DPF is full and the engine computer was not able to complete the regeneration. For regeneration to occur the vehicle needs to reach a combination of predetermined engine rpm, engine temperature and vehicle speed and this would ordinarily require a 40 to 60-minute motorway journey.

 If the DPF warning light does not go out or is accompanied by an Engine Management Light, bring the vehicle to your nearest main dealer immediately. 

Why are DPF’s so Expensive?
The inner components of a DPF are expensive to manufacture as the soot/particulate they filter are so small. The matrix which catches the pollutants is also made from exotic materials such as porous ceramics and silicon carbide. It’s not uncommon for a DPF to cost €1500 for the part alone excluding the labour for fitment..