internal belt and a tensioner...P000b error

[Littlehood1234+]

My mechanic just cleaned the oil pump and changed the internal belt and a tensioner...now my Citroen c3 petrol 12 engine 2014 is working weird..and an error is coming out.before the intervention the error was engine oil pressure fault.now the error changed To engine fault repair needed..what could be the problem?thanks in advance..