The invention relates to online diagnosing of an entity (150) having a plurality of components (c 1 ,..., c n ) whose respective health statuses (s) are to be determined. An online diagnosis engine (100) adapted to execute a fault isolation algorithm includes an input interface (130) and a processing unit (110). The input interface (130) receives results ({R t }) of a set of tests (t 1 ,..., t x ) performed in respect of the components (c 1 ,..., c n ). The processing unit (110) generates, in real time, a status report ( ) reflecting a functional quality of each of said components (c 1 ,..., c n ) based on the test results ({R t }) currently available on the input interface (130). In this procedure, the processing unit (110) implements simplified Boolean functions representing a truth-table of all possible combinations of test results ({R t }) and their status reports ( ).