A notion of diagnosability for hybrid systems is defined, which generalizes the notion of observability. We verify bility properties on a timed automaton abstraction of the original hybrid system. We propose a procedure to check diagnosability, and show that the complexity of the verification is in PTIME for the system class of our abstraction, namely for a subclass of timed automata: the durational graphs. We apply our procedure to an electromagnetic valve system for camless engines.