page about gearbox
See also: AutoTrans for automatic gearboxes.
Manual gearboxes have little connection with the ECM, sometimes there are switches for each gear (or just 0 and Reverse).
Gearbox maintenance have it's own tools and knowledge, model-specific expertise often comes handy. Anyway, it's nice to have some general gearbox education.
"there are many parts in a gearbox" - MembersPage/MichaelKristensen after disassembling his MG's gearbox :-)