citroen 05 2.0 hdi limp mode ?

hi drove my van from Poland to u.k no bother ,on the subsequent drive back it went into limp mode i.e would not rev beyond a certain point, this continued till we go home when the next day i started it up and all was good again ? no problems since i think i need a code reader,but which reader? would anyone recommend any!! i am at a loss as to why this occurred and can only put it down to the rain we drove through on the way home any help would be gratefully accepted thanks...other than this the van has been serviced and is done 80k all in good order