What, has something changed in recent times? Last time I had a 'service' light go off, I went to the store and bought a CAN/ODB2 scanner that
did *way* more than I actually needed. (It was the fanciest one they
had at around $100) You can just visit a parts store
and they will go out and hook up a scanner for free. It pinpointed the
problem system and the repair was easy.
Besides, on a 'modern' car, most of the repairs are replacing consumables
like brakes, rotors, shocks, filters, exhaust, tires, etc. Maybe if you
specialize in fancier repairs/enhancements like transmission and engine
rebuilds or modifications you might need special tools.