That would be your call. For me as I do automotive for a living that makes sense - however to someone who does not may make it more confusing.
Personally, I would sort the categories/sections in the same order that they are in the FSM or FAST - however sorting in alphabetical may be simpler for others.
If going via FSM would be something like:
GI - General Info
MA - Maintenance
...
MT - Manual Trans
AT - Auto Trans
FA - Front Axle
RA - Rear Axle
BR - Brake System
ST - Steering System
....
Etc... Etc...
Reference:
http://www.nicoclub.com/FSM/Sentra/1995_Sentra/fwd.pdf
In a technical area my thought is by having it the same as the FSM it makes it easier for users to find in the FSMs and more so to ENCOURAGE PEOPLE TO READ THEIR FSM.
STATUS: Happy I don't have to make this decision.