Driver ignorance could end up pushing petrol costs back on the agenda of fleets if diesel particulate filters (DPFs) continue to present issues. Vehicle manufacturers have said that there is only one major issue with DPF technology at this time: when the exhaust doesn't heat up enough to burn off collected soot.æ This can then block the filter and cause the dashboard warning light to come on.æ This particular problem is more common during shorter trips in stop-start environments. A DPF has been a standard fit on new cars since 2000 when the Euro 5 exhaust emission standards came into force.æ Many cars registered before the new regulations came in were also fitted in anticipation of the changing standards. The aim of the laws were to deliver an 80 per cent reduction in soot emissions, but the technology is known for causing some problems.æ AA patrols are regularly called out to cars showing a warning light as a result of a partially blocked filter. Jo Hammonds, fleet manager for Mears Group _ which operates around 1,200 vehicles in the M25 area _ said: 'For the larger vans it's not so much of an issue as you will have to take diesel, but for the car-derived vans do we go for a 1.1-litre to 1.2-litre petrol or a 1.4-litre diesel?î 'Petrol is very much back on the agenda and I think problems with DPFs will sway policy for us in central London.î The Salvation Army were one fleet to switch to petrol in 2010.æ Fleet co-ordinator, Peter Bonney said that DPF problems began with some of the Euro 4 technology. 'We understood Euro 5 was bringing them in, but what we didn't know was to achieve Euro 4 some manufacturers had fitted DPFs,î he said. 'Manufacturers were not communicating what the issues were with us.î The AA currently advises the importance of reading the relevant section of the handbook in any vehicle where a DPF is fitted so the driver can understand which actions they need to need if the warning light shows.