We present a new generic diagnostic engine to diagnose systems that are modelled with first order logic. The originality of this engine is that it takes benefit of recent advances in constraint programming to perform satisfiability tests by the use of an off-the- shelf CSP solver. The second contribution of this paper is the defi- nition of an incremental search strategy that deals with the intrinsic complexity of the problem to look for minimal diagnoses in complex digital systems. The use of the DITO engine and its strategy is fully illustrated on the c6288 circuit that is part of the classical ISCAS85 benchmark.