The courtesy lights don't work, the trunk light doesn't work, the air conditioning doesn't work, the rear window defroster doesn't work, the home link doesn't work, the air bag light is on, the track off light is on, the BATTERY STATE shows four question marks (????), and the fuel usage calculation is way off.
Several items quit working at the same time the SERVICE VEHICLE SOON light lit. on 1999 Buick Park Avenue
you may have several issues but start by scanning codes and posting so we can adv