You COULD have done aGogle search.
Some stuff I found (plus some dedicated Pug forums, which may be of more help)
http://www.honestjohn.co.uk/forum/post/?t=91263
http://www.peugeotforums.com/forums/maintenance-9/peugeot-407-depollution-system-faulty-347/ (Especially last post)
http://www.peugeotcentral.co.uk/ftopic-9185.html
HTH
March 2017