There is no check engine or Mil light on these.The car does have a limited self diagnostic function,but it is not like a later 16 pin Obd system.This car runs an old 38 pin diagnostic connector which requires an old style machine.for diagnostics. The throttle control on these is part mechanical cable and part electronic throttle body. You really need to find a good indy Merc specialist that understands the operation of these older systems.