1 press button from 4wd low to 4 wd high before going to 3 wd
2 make sure tranny is in N or try inR backing slowly
3 there are 3 parts to system,,,switch,,,solenoid,,,actuator
i had my 99 s 10 refuse to shift into 4wd,,,,actuator and solenoid cost 150 to replace,,,90 parts,,60 labor