Fiat Doblo key code

hi
guys me again i have had this problem for a few months now my doblo has intermitten starting problems ive had the reader changed and a bought a new key .and i still have the old key but the problem is the same .iv'e been told it could be a keycode unit some where nwear the fuse box or behind a panel but i cannot see anything and i don't know what i'm looking for can anybody help pls if i go to fiat and have a diagnostic the fault will only show up if it has a problem while in the garage .but if it doesn't have a problem while in the shop a diagnostic problem won't show up
well this is what iv'e been told can anybody help its doin my swede in ??????