You dont need to remove the engine. if its 1.4 hdi diesel remove airfilter and airfilter housing to gain access to the plugs on the back of the engine if its 1.9 non hdi diesel remove the black plastic air intake manifold i work on if its 2.0 hdi they the easiest i work on Peugeots all the time and have never removed an engine yet to get at heater plugs
Peugeot master technician, November 2008