A method for detecting faults and their locations in an optical path between an optical line terminal (OLT) of and optical network units (ONUs) of a passive optical network (PON). The method comprises forming a maintenance optical link through the PON between the OLT and a collocated ONU, the OLT and its collocated ONU are each connected to an optical splitter; sending a ranging request from the OLT to the collocated ONU; in response to the ranging request, receiving, over the maintenance optical line, a ranging burst signal including at least a fault analysis detection pattern (FADP); and analyzing the FADP in the received signal by auto-correlating the FADP signal with an expected FADP signal, an uncorrelated event measured through the auto-correlation is indicative of a fault in the optical path of the PON and occurrence times of such events are indicative of the fault's location in the optical path.