New emissions rules could spell unforeseen costs for operators - sparking caution and lower residual values in the used market.

That is the warning from John Watts, of used van pricing experts, CAP.

Compliance with the new Euro 5 emissions legislation relies partly on the use of diesel particulate filters and this poses particular problems for owners restricting their operations to short-distance urban work.

Such filters can easily clog under the typical operating conditions faced in cities, spelling expensive repairs or replacement parts. This is likely to spark caution in the future used market, due to the ‘invisible' nature of such problems - meaning trade buyers will factor in the risk of a clogged particulate filter when determining the price they will offer for a used Euro 5 van.

Watts explained: "Many diesel particulate filters require specific drive cycles in order to remain working efficiently. These filters need to reach a certain operating temperature before effectively reducing particulate emissions, but if this is not achieved they can become prone to clogging.

"This problem will mostly emerge in low speed, short distance operating cycles, typically undertaken in large conurbations. This type of operating environment could become even more of a problem for future owners since operational radius tends to reduce in the secondary market.

"A typical example could be a city-based self-employed used van owner who travels less than ten miles to site from home and stays all day. A continuous operation of this nature could result in a blocked filter and a potential replacement cost.

"Most manufacturers issue guidelines about how to prevent total blockage. This usually consists of driving the vehicle at speed for a minimum time period in order for the filter to reach operating temperature so that it can burn off the carbon particulates. The need for this is usually indicated by a dashboard warning light. If this warning is continually ignored, permanent blockage can follow with subsequent filter replacement.

"There are several potential problems for the future used market. How will subsequent owners be made aware of this issue, especially when many vehicle handbooks are not present at the time of ownership change? If problems occur, how many will take their vehicles back to the supplier, expecting them to carry out repairs under warranty? Following on from that, how will the trade view vehicle values in the light of potential problems of this nature?

"CAP's view is that the used vehicle trade need to be aware of the potential problem and ensure that vehicle documentation is complete, especially where a filter has already been replaced. Used van buyers in turn must be aware of the need for a functioning particulate filter for Euro 5 compliance and that problems may not be routinely covered under warranty."