Had this fault on a Peugeot Boxer - same engine - and, as you say, the DEC high pressure pump replacement routine doesn't look like it's working. But, if you then try the same with KTS it throws a code for HP pump not calibrated correctly. When I then tried again with the DEC this code disappeared which makes me think it is actually working although it throws up an error message at the end.

Roman at DEC is working on this one

Dick