Yes, short journeys will inevitably cause issues as diesel cars aren't intended for this kind of use. Diesel engines produce a lot of soot - also called particulate matter (PM) - when they burn fuel. The job of the DPF is to filter and store this soot - which can cause harmful health issues - in order to reduce emissions from diesel cars. But because they have a limited capacity, this soot has to be regularly burned off to regenerate the DPF. If the soot blocks the filter, this can stop the engine from running and leave you with a hefty repair bill for either cleaning or replacing the DPF. Going for a 40-minute motorway drive should your DPF filter in good condition as it'll get hot enough to burn off this soot and prevent it getting blocked up, but I would also suggest reading this guide for a better overall understanding of how to keep your car and your DPF running well: heycar.co.uk/guides/what-is-a-diesel-particulate-f...f--