If a Preliminary Evaluation determines there may be deeper problems, an Engineering Analysis continues the examination and looks more in-depth at a potential problem or defect. This is the step that requires the technical expertise and perspective of experts currently called into question by Toyota's hearings.
Simply put, there are too few experts to handle many of these issues, particularly now that a lot of problems in vehicles are software-related, not mechanical-related.
This is the last step before a recall, and the two possible outcomes are closure of the investigation, or an escalation to a recall.