I have heard several stories about these getting clogged up and having to be replaced. I read this today about a possible cure, some may be interested...
http://blog.warrantydirect.co.uk/2014/03/19/dont-delete-your-dpf-clean-it/?utm_campaign=eNews+April+14+&utm_source=emailCampaign&utm_medium=email&utm_content=#.Uzr3wahdWZh
http://blog.warrantydirect.co.uk/2014/03/19/dont-delete-your-dpf-clean-it/?utm_campaign=eNews+April+14+&utm_source=emailCampaign&utm_medium=email&utm_content=#.Uzr3wahdWZh