Abstract: A diagnostic and maintenance support system and process to that performs tests on systems, collects Built-In-Test (BIT) log data, analyzes fault data, and recommends Shop Replaceable Units (SRUs). The system hardware may include a computer, an interface test adapter, and a cable set. A process performs a Discrete Fault Mask (DFM) algorithm to determine whether a single faulty SRU can be identified; a Combinational Fault Mask (CFM) algorithm to identify a list of potentially problematic SRU's if a matching bit is not found after the DFM algorithm is performed; and a source code segment stored within memory of the computer for performing a Reserved Fault Mask (RFM) algorithm to identify a list of potentially problematic SRU's if matching bits are not found between the retrieved fault signature and the list of CFM serial words representing ambiguous tests. The system further includes a Diagnostic Database stored within memory of the computer which includes a DFM Table, a CFM Table and a RSM Table.