93 land curiser shift override

93 land curiser. started having porblems where to get it out of park, the shift override button has to be held down while shifting out of park. after that you are able to shift in other gears without the help from the shift override button. if the button is not held down you wont be able to move out of park and only park. is this a common problem? where should i start to fix the problem? what causes this?