A diagnostic and maintenance support system and process are provided for performing tests, collecting Built-In-Test (BIT) log data from systems, analyzing fault data, and recommending Shop Replaceable Units (SRU's). The system and process include uploading and reading a retrieved fault signature from a BIT log retrieved from a subject system under test. The retrieved fault signature is a serial word composed of a plurality of consecutive bits indicating either a pass or fail. Each bit is assigned to a specific SRU, system level test, or an event. The system and process further include a source code segment for performing a Discrete Fault Mask (DFM) algorithm, a Combinational Fault Mask (CFM) algorithm, and a source code segment 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.