look at your shift knop on if it is auto and there is press in button that you can push in to go in or out. If the O/D light is on no matter what you do with the button you might have some sort of problem.
5 ? ........ P11 autos have 4 speed boxes....... It shifts to 4th @ 42/43 Mph under light accelaration ...... OD light on means Your "Overdrive is turned off" Ideally teh light should be out (& therefor the function is on) ....... RTFM :beard: