The A320 family relies on engineers interrogating systems through the mcdu to troubleshoot systems and a lot of the old fashioned engineering practices and knowledge are slowly becoming a lost art,imho.
Having spent a number of years closely associated with Naval Aviation maintenance on what are now ancient aircraft the following observations may be relevant.
The worst troubleshooting problems tend to be in things like connectors, and damaged wire bundles. In cases where the box has to slide in to a rack and mate to a connector on the back side, things like recessed pins and bent pins can do weird things to connections. Even a minor obstruction could keep a box from fully seating on its associated connector with rear mount connections.
Wires can be open, shorted, or cross connected to another wire. Flexing of the airframe and unequal thermal expansion between wires and airframe can impose stresses that eventually damage improperly positioned wire bundles as can adjacent maintenance activity. Access and visibility are typically difficult in aircraft and can mask otherwise simple problems.
Intermittent problems are particularly difficult because they generally do not present themselves for correction on the ground. It frequently can require someone with an electrical engineering background to infer what the problem must be based on the symptoms. In those cases, the more data, the better.
Aviation has relied on easily replaceable boxes to facilitate maintenance for many years, and the advent of computerized troubleshooting improves the odds of fixing a problem accurately but airframe side of the interface problems are another story. Problem is, unsolved technical problems can add to the Swiss Cheese holes that eventually cause an accident.